[llvm] [InstCombine] Invalidate changes to `DoesConsume` if the first try fails (PR #82973)

[via llvm-commits]

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@@ -0,0 +1,40 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 4
+; RUN: opt -S -passes=instcombine < %s | FileCheck %s
+
+define i64 @func(i32 %p) {
+; CHECK-LABEL: define i64 @func(
+; CHECK-SAME: i32 [[P:%.*]]) {
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[NOT:%.*]] = xor i32 [[P]], -1
+; CHECK-NEXT:    br label [[FOR_BODY:%.*]]
+; CHECK:       for.body:
+; CHECK-NEXT:    [[P0:%.*]] = phi i32 [ [[NOT]], [[ENTRY:%.*]] ], [ [[CONV:%.*]], [[FOR_BODY]] ]
+; CHECK-NEXT:    [[P1:%.*]] = phi i32 [ 0, [[ENTRY]] ], [ [[INC:%.*]], [[FOR_BODY]] ]
+; CHECK-NEXT:    [[INC]] = add i32 [[P1]], 1
+; CHECK-NEXT:    [[CMP1_NOT:%.*]] = icmp eq i32 [[INC]], 0
+; CHECK-NEXT:    [[COND:%.*]] = select i1 [[CMP1_NOT]], i32 -1231558963, i32 0
+; CHECK-NEXT:    [[XOR:%.*]] = xor i32 [[COND]], [[P0]]
+; CHECK-NEXT:    [[CMP2:%.*]] = icmp ne i32 [[XOR]], -2
+; CHECK-NEXT:    [[CONV]] = zext i1 [[CMP2]] to i32
+; CHECK-NEXT:    br i1 [[CMP2]], label [[FOR_BODY]], label [[FOR_EXIT:%.*]]
+; CHECK:       for.exit:
+; CHECK-NEXT:    ret i64 0
+;
+entry:
+  %not = xor i32 %p, -1
+  br label %for.body
+
+for.body:
+  %p0 = phi i32 [ %not, %entry ], [ %conv, %for.body ]
+  %p1 = phi i32 [ 0, %entry ], [ %inc, %for.body ]
+  %inc = add i32 %p1, 1
+  %cmp1 = icmp ne i32 %inc, 0
+  %cond = select i1 %cmp1, i32 0, i32 -1231558963
+  %xor = xor i32 %cond, %p0
+  %cmp2 = icmp ne i32 %xor, -2
+  %conv = zext i1 %cmp2 to i32
+  br i1 %cmp2, label %for.body, label %for.exit
+
+for.exit:
+  ret i64 0
+}
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goldsteinn wrote:

or just use `call void @llvm.sideeffect()`

https://github.com/llvm/llvm-project/pull/82973