[llvm] [Utils][Local] Preserve !nosanitize in combineMetadata when merging instructions (PR #148376)

[Nikita Popov via llvm-commits]

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@@ -409,6 +409,31 @@ join:
   ret void
 }
 
+define void @test_nosanitize(ptr %p) {
+; CHECK-LABEL: define void @test_nosanitize
+; CHECK-SAME: (ptr [[P:%.*]]) {
+; CHECK-NEXT:    [[V1:%.*]] = load i32, ptr [[P]], align 4, !nosanitize [[META6]]
+; CHECK-NEXT:    [[COND:%.*]] = icmp eq i32 [[V1]], 0
+; CHECK-NEXT:    br i1 [[COND]], label [[IF:%.*]], label [[JOIN:%.*]]
+; CHECK:       if:
+; CHECK-NEXT:    call void @use.i32(i32 0)
+; CHECK-NEXT:    br label [[JOIN]]
+; CHECK:       join:
+; CHECK-NEXT:    ret void
+;
+  %v1 = load i32, ptr %p, !nosanitize !11
+  %cond = icmp eq i32 %v1, 0
+  br i1 %cond, label %if, label %join
+
+if:
+  %v2 = load i32, ptr %p, !nosanitize !11
+  call void @use.i32(i32 %v2)
+  br label %join
+
+join:
+  ret void
+}
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nikic wrote:

It depends a bit on the intended purpose of !nosanitize (which is, of course, not documented in LangRef). My initial assumption was that !nosanitize means "this must not be sanitized", but looking at how this actually appears to be used is "sanitization can be omitted for performance reasons". With that in mind, I agree with your interpretation.

https://github.com/llvm/llvm-project/pull/148376