[llvm] [AA] Refine ModRefInfo taking into account `errnomem` location (PR #157495)

[Nikita Popov via llvm-commits]

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@@ -0,0 +1,133 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -S -passes=instcombine < %s | FileCheck %s
+
+; sinf clobbering errno, but %p cannot alias errno per C/C++ strict aliasing rules via TBAA.
+; Can do constant store-to-load forwarding.
+define float @does_not_alias_errno(ptr %p, float %f) {
+; CHECK-LABEL: define float @does_not_alias_errno(
+; CHECK-SAME: ptr [[P:%.*]], float [[F:%.*]]) {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    store float 0.000000e+00, ptr [[P]], align 4, !tbaa [[TBAA4:![0-9]+]]
+; CHECK-NEXT:    [[CALL:%.*]] = call float @sinf(float [[F]])
+; CHECK-NEXT:    ret float 0.000000e+00
+;
+entry:
+  store float 0.000000e+00, ptr %p, align 4, !tbaa !4
+  %call = call float @sinf(float %f)
+  %0 = load float, ptr %p, align 4, !tbaa !4
+  ret float %0
+}
+
+; sinf clobbering errno, but %p is alloca memory, wich can never aliases errno.
+; Can do constant store-to-load forwarding.
+define float @does_not_alias_errno_2(float %f) {
+; CHECK-LABEL: define float @does_not_alias_errno_2(
+; CHECK-SAME: float [[F:%.*]]) {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    [[P:%.*]] = alloca float, align 4
+; CHECK-NEXT:    call void @escape(ptr nonnull [[P]])
+; CHECK-NEXT:    store float 0.000000e+00, ptr [[P]], align 4
+; CHECK-NEXT:    [[TMP1:%.*]] = call float @sinf(float [[F]])
+; CHECK-NEXT:    ret float 0.000000e+00
+;
+entry:
+  %p = alloca float
+  call void @escape(ptr %p)
+  store float 0.0, ptr %p
+  call float @sinf(float %f)
+  %v = load float, ptr %p
+  ret float %v
+}
+
+; sinf clobbering errno, but %p is memory accessed w/ size larger than errno.
+; Can do constant store-to-load forwarding.
+define double @does_not_alias_errno_3(ptr %p, float %f) {
+; CHECK-LABEL: define double @does_not_alias_errno_3(
+; CHECK-SAME: ptr [[P:%.*]], float [[F:%.*]]) {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    call void @escape(ptr [[P]])
+; CHECK-NEXT:    store double 0.000000e+00, ptr [[P]], align 8
+; CHECK-NEXT:    [[TMP1:%.*]] = call float @sinf(float [[F]])
+; CHECK-NEXT:    ret double 0.000000e+00
+;
+entry:
+  call void @escape(ptr %p)
+  store double 0.0, ptr %p
+  call float @sinf(float %f)
+  %v = load double, ptr %p
+  ret double %v
+}
+
+; %p may alias errno, but cosf does not clobber errno.
+; Can do constant store-to-load forwarding.
+define float @may_alias_errno_does_not_clobber(ptr %p, float %f) {
+; CHECK-LABEL: define float @may_alias_errno_does_not_clobber(
+; CHECK-SAME: ptr [[P:%.*]], float [[F:%.*]]) {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    store float 0.000000e+00, ptr [[P]], align 4
+; CHECK-NEXT:    [[CALL:%.*]] = call float @cosf(float [[F]])
+; CHECK-NEXT:    ret float 0.000000e+00
+;
+entry:
+  store float 0.000000e+00, ptr %p, align 4
+  %call = call float @cosf(float %f)
+  %0 = load float, ptr %p, align 4
+  ret float %0
+}
+
+; sinf clobbering errno, unknown TBAA info, %p may alias errno.
+; Cannot do constant store-to-load forwarding.
+define float @may_alias_errno(ptr %p, float %f) {
+; CHECK-LABEL: define float @may_alias_errno(
+; CHECK-SAME: ptr [[P:%.*]], float [[F:%.*]]) {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    store float 0.000000e+00, ptr [[P]], align 4
+; CHECK-NEXT:    [[CALL:%.*]] = call float @sinf(float [[F]])
+; CHECK-NEXT:    [[TMP0:%.*]] = load float, ptr [[P]], align 4
+; CHECK-NEXT:    ret float [[TMP0]]
+;
+entry:
+  store float 0.000000e+00, ptr %p, align 4
+  %call = call float @sinf(float %f)
+  %0 = load float, ptr %p, align 4
+  ret float %0
+}
+
+; sinf clobbering errno, %p, a integer pointer, may alias errno.
+; Cannot do constant store-to-load forwarding.
+define i32 @may_alias_errno_2(ptr %p, float %f) {
+; CHECK-LABEL: define i32 @may_alias_errno_2(
+; CHECK-SAME: ptr [[P:%.*]], float [[F:%.*]]) {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    store i32 0, ptr [[P]], align 4, !tbaa [[TBAA0:![0-9]+]]
+; CHECK-NEXT:    [[CALL:%.*]] = call float @sinf(float [[F]])
+; CHECK-NEXT:    [[TMP0:%.*]] = load i32, ptr [[P]], align 4, !tbaa [[TBAA0]]
+; CHECK-NEXT:    ret i32 [[TMP0]]
+;
+entry:
+  store i32 0, ptr %p, align 4, !tbaa !0
+  %call = call float @sinf(float %f)
+  %0 = load i32, ptr %p, align 4, !tbaa !0
+  ret i32 %0
+}
+
+declare float @sinf(float) memory(errnomem: write)
+declare float @cosf(float) memory(argmem: write, errnomem: read)
----------------
nikic wrote:

I'd use a function other than cosf for this. It's confusing, as the actual cosf wouldn't have these memory effects...

https://github.com/llvm/llvm-project/pull/157495