[CodeGenPrepare] Bail out of usubo creation if sub's parent is not the same as the comparison (#160358)

We match uadd's behavior here.

Codegen comparison: https://godbolt.org/z/x8j4EhGno

1 files changed, 6 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/CodeGenPrepare.cpp b/llvm/lib/CodeGen/CodeGenPrepare.cpp
index d290f20..eb73d01b 100644
--- a/llvm/lib/CodeGen/CodeGenPrepare.cpp
+++ b/llvm/lib/CodeGen/CodeGenPrepare.cpp
@@ -1749,6 +1749,12 @@ bool CodeGenPrepare::combineToUSubWithOverflow(CmpInst *Cmp,
                                  Sub->hasNUsesOrMore(1)))
     return false;
 
+  // We don't want to move around uses of condition values this late, so we
+  // check if it is legal to create the call to the intrinsic in the basic
+  // block containing the icmp.
+  if (Sub->getParent() != Cmp->getParent() && !Sub->hasOneUse())
+    return false;
+
   if (!replaceMathCmpWithIntrinsic(Sub, Sub->getOperand(0), Sub->getOperand(1),
                                    Cmp, Intrinsic::usub_with_overflow))
     return false;