[llvm] 8fc9eea - Test that volatile load type isn't changed
JF Bastien via llvm-commits
llvm-commits at lists.llvm.org
Mon Mar 9 11:22:25 PDT 2020
Author: JF Bastien
Date: 2020-03-09T11:19:23-07:00
New Revision: 8fc9eea43a94d83e46614eee47b069e25848fedb
URL: https://github.com/llvm/llvm-project/commit/8fc9eea43a94d83e46614eee47b069e25848fedb
DIFF: https://github.com/llvm/llvm-project/commit/8fc9eea43a94d83e46614eee47b069e25848fedb.diff
LOG: Test that volatile load type isn't changed
Summary: As discussed in D75505, it's not particularly useful to change the type of a load to/from floating-point/integer because it's followed by a bitcast, and it might lead to surprising code generation. Check that this doesn't generally happen.
Reviewers: lebedev.ri
Subscribers: jkorous, dexonsmith, ributzka, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D75644
Added:
llvm/test/Transforms/InstCombine/volatile_load_cast.ll
Modified:
llvm/docs/LangRef.rst
Removed:
################################################################################
diff --git a/llvm/docs/LangRef.rst b/llvm/docs/LangRef.rst
index 5ad97fb87267..480a0fc4c07a 100644
--- a/llvm/docs/LangRef.rst
+++ b/llvm/docs/LangRef.rst
@@ -2456,10 +2456,11 @@ The compiler may assume execution will continue after a volatile operation,
so operations which modify memory or may have undefined behavior can be
hoisted past a volatile operation.
-IR-level volatile loads and stores cannot safely be optimized into
-llvm.memcpy or llvm.memmove intrinsics even when those intrinsics are
-flagged volatile. Likewise, the backend should never split or merge
-target-legal volatile load/store instructions.
+IR-level volatile loads and stores cannot safely be optimized into llvm.memcpy
+or llvm.memmove intrinsics even when those intrinsics are flagged volatile.
+Likewise, the backend should never split or merge target-legal volatile
+load/store instructions. Similarly, IR-level volatile loads and stores cannot
+change from integer to floating-point or vice versa.
.. admonition:: Rationale
diff --git a/llvm/test/Transforms/InstCombine/volatile_load_cast.ll b/llvm/test/Transforms/InstCombine/volatile_load_cast.ll
new file mode 100644
index 000000000000..7eb0a5427c92
--- /dev/null
+++ b/llvm/test/Transforms/InstCombine/volatile_load_cast.ll
@@ -0,0 +1,59 @@
+; RUN: opt < %s -instcombine -S | FileCheck %s
+
+; Ensure that volatile loads followed by a bitcast don't get transformed into a
+; volatile load of the bitcast-target type. This is unlikely to provide much in
+; terms of optimizations, and might break the programmer's expectation for code
+; generation, however brittle that expectation might be.
+;
+; See llvm.org/D75644 and llvm.org/D75505
+target datalayout = "e-p:64:64-i32:32:32-i64:64:64-f32:32:32-f64:64:64"
+
+define float @float_load(i32* %addr) {
+; CHECK-LABEL: @float_load(
+; CHECK: %i32 = load volatile i32, i32* %addr, align 4
+; CHECK-NEXT: %float = bitcast i32 %i32 to float
+; CHECK-NEXT: ret float %float
+ %i32 = load volatile i32, i32* %addr, align 4
+ %float = bitcast i32 %i32 to float
+ ret float %float
+}
+
+define i32 @i32_load(float* %addr) {
+; CHECK-LABEL: @i32_load(
+; CHECK: %float = load volatile float, float* %addr, align 4
+; CHECK-NEXT: %i32 = bitcast float %float to i32
+; CHECK-NEXT: ret i32 %i32
+ %float = load volatile float, float* %addr, align 4
+ %i32 = bitcast float %float to i32
+ ret i32 %i32
+}
+
+define double @double_load(i64* %addr) {
+; CHECK-LABEL: @double_load(
+; CHECK: %i64 = load volatile i64, i64* %addr, align 8
+; CHECK-NEXT: %double = bitcast i64 %i64 to double
+; CHECK-NEXT: ret double %double
+ %i64 = load volatile i64, i64* %addr, align 8
+ %double = bitcast i64 %i64 to double
+ ret double %double
+}
+
+define i64 @i64_load(double* %addr) {
+; CHECK-LABEL: @i64_load(
+; CHECK: %double = load volatile double, double* %addr, align 8
+; CHECK-NEXT: %i64 = bitcast double %double to i64
+; CHECK-NEXT: ret i64 %i64
+ %double = load volatile double, double* %addr, align 8
+ %i64 = bitcast double %double to i64
+ ret i64 %i64
+}
+
+define i8* @ptr_load(i64* %addr) {
+; CHECK-LABEL: @ptr_load(
+; CHECK: %i64 = load volatile i64, i64* %addr, align 8
+; CHECK-NEXT: %ptr = inttoptr i64 %i64 to i8*
+; CHECK-NEXT: ret i8* %ptr
+ %i64 = load volatile i64, i64* %addr, align 8
+ %ptr = inttoptr i64 %i64 to i8*
+ ret i8* %ptr
+}
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