Disable jump threading of float equality
Resolves: RHEL-54025
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0001-Disable-jump-threading-of-float-equality.patch
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212
0001-Disable-jump-threading-of-float-equality.patch
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From 49166c7dd925244f631277b4aa9ae4233f300884 Mon Sep 17 00:00:00 2001
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From: Nilstrieb <48135649+Nilstrieb@users.noreply.github.com>
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Date: Sat, 27 Jul 2024 15:08:11 +0200
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Subject: [PATCH] Disable jump threading of float equality
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Jump threading stores values as `u128` (`ScalarInt`) and does its
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comparisons for equality as integer comparisons.
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This works great for integers. Sadly, not everything is an integer.
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Floats famously have wonky equality semantcs, with `NaN!=NaN` and
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`0.0 == -0.0`. This does not match our beautiful integer bitpattern
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equality and therefore causes things to go horribly wrong.
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While jump threading could be extended to support floats by remembering
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that they're floats in the value state and handling them properly,
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it's signficantly easier to just disable it for now.
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(cherry picked from commit eca0a7e72346ba123ace318a0f9c28c57d990aeb)
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---
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.../rustc_mir_transform/src/jump_threading.rs | 7 +++
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...ding.floats.JumpThreading.panic-abort.diff | 59 +++++++++++++++++++
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...ing.floats.JumpThreading.panic-unwind.diff | 59 +++++++++++++++++++
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tests/mir-opt/jump_threading.rs | 12 ++++
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4 files changed, 137 insertions(+)
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create mode 100644 tests/mir-opt/jump_threading.floats.JumpThreading.panic-abort.diff
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create mode 100644 tests/mir-opt/jump_threading.floats.JumpThreading.panic-unwind.diff
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diff --git a/compiler/rustc_mir_transform/src/jump_threading.rs b/compiler/rustc_mir_transform/src/jump_threading.rs
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index a458297210db..e2d2864ad2a0 100644
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--- a/compiler/rustc_mir_transform/src/jump_threading.rs
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+++ b/compiler/rustc_mir_transform/src/jump_threading.rs
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@@ -493,6 +493,13 @@ fn process_assign(
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BinOp::Ne => ScalarInt::FALSE,
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_ => return None,
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};
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+ if value.const_.ty().is_floating_point() {
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+ // Floating point equality does not follow bit-patterns.
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+ // -0.0 and NaN both have special rules for equality,
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+ // and therefore we cannot use integer comparisons for them.
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+ // Avoid handling them, though this could be extended in the future.
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+ return None;
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+ }
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let value = value.const_.normalize(self.tcx, self.param_env).try_to_scalar_int()?;
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let conds = conditions.map(self.arena, |c| Condition {
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value,
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diff --git a/tests/mir-opt/jump_threading.floats.JumpThreading.panic-abort.diff b/tests/mir-opt/jump_threading.floats.JumpThreading.panic-abort.diff
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new file mode 100644
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index 000000000000..6ca37e96d297
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--- /dev/null
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+++ b/tests/mir-opt/jump_threading.floats.JumpThreading.panic-abort.diff
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@@ -0,0 +1,59 @@
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+- // MIR for `floats` before JumpThreading
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++ // MIR for `floats` after JumpThreading
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+
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+ fn floats() -> u32 {
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+ let mut _0: u32;
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+ let _1: f64;
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+ let mut _2: bool;
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+ let mut _3: bool;
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+ let mut _4: f64;
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+ scope 1 {
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+ debug x => _1;
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+ }
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+
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+ bb0: {
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+ StorageLive(_1);
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+ StorageLive(_2);
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+ _2 = const true;
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+- switchInt(move _2) -> [0: bb2, otherwise: bb1];
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++ goto -> bb1;
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+ }
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+
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+ bb1: {
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+ _1 = const -0f64;
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+ goto -> bb3;
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+ }
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+
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+ bb2: {
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+ _1 = const 1f64;
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+ goto -> bb3;
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+ }
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+
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+ bb3: {
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+ StorageDead(_2);
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+ StorageLive(_3);
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+ StorageLive(_4);
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+ _4 = _1;
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+ _3 = Eq(move _4, const 0f64);
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+ switchInt(move _3) -> [0: bb5, otherwise: bb4];
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+ }
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+
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+ bb4: {
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+ StorageDead(_4);
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+ _0 = const 0_u32;
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+ goto -> bb6;
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+ }
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+
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+ bb5: {
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+ StorageDead(_4);
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+ _0 = const 1_u32;
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+ goto -> bb6;
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+ }
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+
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+ bb6: {
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+ StorageDead(_3);
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+ StorageDead(_1);
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+ return;
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+ }
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+ }
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+
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diff --git a/tests/mir-opt/jump_threading.floats.JumpThreading.panic-unwind.diff b/tests/mir-opt/jump_threading.floats.JumpThreading.panic-unwind.diff
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new file mode 100644
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index 000000000000..6ca37e96d297
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--- /dev/null
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+++ b/tests/mir-opt/jump_threading.floats.JumpThreading.panic-unwind.diff
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@@ -0,0 +1,59 @@
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+- // MIR for `floats` before JumpThreading
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++ // MIR for `floats` after JumpThreading
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+
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+ fn floats() -> u32 {
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+ let mut _0: u32;
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+ let _1: f64;
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+ let mut _2: bool;
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+ let mut _3: bool;
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+ let mut _4: f64;
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+ scope 1 {
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+ debug x => _1;
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+ }
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+
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+ bb0: {
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+ StorageLive(_1);
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+ StorageLive(_2);
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+ _2 = const true;
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+- switchInt(move _2) -> [0: bb2, otherwise: bb1];
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++ goto -> bb1;
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+ }
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+
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+ bb1: {
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+ _1 = const -0f64;
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+ goto -> bb3;
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+ }
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+
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+ bb2: {
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+ _1 = const 1f64;
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+ goto -> bb3;
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+ }
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+
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+ bb3: {
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+ StorageDead(_2);
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+ StorageLive(_3);
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+ StorageLive(_4);
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+ _4 = _1;
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+ _3 = Eq(move _4, const 0f64);
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+ switchInt(move _3) -> [0: bb5, otherwise: bb4];
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+ }
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+
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+ bb4: {
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+ StorageDead(_4);
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+ _0 = const 0_u32;
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+ goto -> bb6;
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+ }
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+
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+ bb5: {
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+ StorageDead(_4);
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+ _0 = const 1_u32;
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+ goto -> bb6;
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+ }
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+
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+ bb6: {
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+ StorageDead(_3);
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+ StorageDead(_1);
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+ return;
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+ }
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+ }
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+
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diff --git a/tests/mir-opt/jump_threading.rs b/tests/mir-opt/jump_threading.rs
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index 57f4e4a2654f..3e7e8995f1a3 100644
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--- a/tests/mir-opt/jump_threading.rs
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+++ b/tests/mir-opt/jump_threading.rs
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@@ -514,6 +514,16 @@ fn assume(a: u8, b: bool) -> u8 {
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)
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}
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+fn floats() -> u32 {
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+ // CHECK-LABEL: fn floats(
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+ // CHECK: switchInt(
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+
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+ // Test for issue #128243, where float equality was assumed to be bitwise.
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+ // When adding float support, it must be ensured that this continues working properly.
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+ let x = if true { -0.0 } else { 1.0 };
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+ if x == 0.0 { 0 } else { 1 }
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+}
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+
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fn main() {
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// CHECK-LABEL: fn main(
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too_complex(Ok(0));
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@@ -528,6 +538,7 @@ fn main() {
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disappearing_bb(7);
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aggregate(7);
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assume(7, false);
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+ floats();
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}
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// EMIT_MIR jump_threading.too_complex.JumpThreading.diff
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@@ -542,3 +553,4 @@ fn main() {
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// EMIT_MIR jump_threading.disappearing_bb.JumpThreading.diff
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// EMIT_MIR jump_threading.aggregate.JumpThreading.diff
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// EMIT_MIR jump_threading.assume.JumpThreading.diff
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+// EMIT_MIR jump_threading.floats.JumpThreading.diff
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--
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2.46.0
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Name: rust
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Version: 1.79.0
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Release: 1%{?dist}
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Release: 2%{?dist}
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Summary: The Rust Programming Language
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License: (Apache-2.0 OR MIT) AND (Artistic-2.0 AND BSD-3-Clause AND ISC AND MIT AND MPL-2.0 AND Unicode-DFS-2016)
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# ^ written as: (rust itself) and (bundled libraries)
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@ -160,6 +160,9 @@ Patch7: 0001-Use-an-explicit-x86-64-cpu-in-tests-that-are-sensiti.patch
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# Fix codegen test failure on big endian: https://github.com/rust-lang/rust/pull/126263
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Patch8: 0001-Make-issue-122805.rs-big-endian-compatible.patch
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# https://github.com/rust-lang/rust/pull/128271
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Patch9: 0001-Disable-jump-threading-of-float-equality.patch
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### RHEL-specific patches below ###
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# Simple rpm macros for rust-toolset (as opposed to full rust-packaging)
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@ -634,6 +637,7 @@ rm -rf %{wasi_libc_dir}/dlmalloc/
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%endif
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%patch -P7 -p1
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%patch -P8 -p1
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%patch -P9 -p1
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%if %with disabled_libssh2
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%patch -P100 -p1
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@ -1135,6 +1139,9 @@ timeout -v 30m %{__x} test --no-fail-fast rustfmt || :
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%changelog
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* Tue Aug 13 2024 Josh Stone <jistone@redhat.com> - 1.79.0-2
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- Disable jump threading of float equality
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* Fri Jun 21 2024 Josh Stone <jistone@redhat.com> - 1.79.0-1
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- Update to 1.79.0
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