[llvm] [InstCombine] Detect uadd with overflow idiom (PR #140178)

[Matt Arsenault via llvm-commits]

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@@ -6533,72 +6533,77 @@ bool InstCombinerImpl::OptimizeOverflowCheck(Instruction::BinaryOps BinaryOp,
   llvm_unreachable("Unexpected overflow result");
 }
 
-/// Recognize and process idiom involving test for multiplication
+/// Recognize and process idiom involving test for unsigned
 /// overflow.
 ///
 /// The caller has matched a pattern of the form:
+///   I = cmp u (add(zext A, zext B), V
 ///   I = cmp u (mul(zext A, zext B), V
 /// The function checks if this is a test for overflow and if so replaces
-/// multiplication with call to 'mul.with.overflow' intrinsic.
+/// addition/multiplication with call to the umul intrinsic or the canonical
+/// form of uadd overflow.
 ///
 /// \param I Compare instruction.
-/// \param MulVal Result of 'mult' instruction.  It is one of the arguments of
-///               the compare instruction.  Must be of integer type.
+/// \param Val Result of add/mul instruction.  It is one of the arguments of
+///            the compare instruction.  Must be of integer type.
 /// \param OtherVal The other argument of compare instruction.
 /// \returns Instruction which must replace the compare instruction, NULL if no
 ///          replacement required.
-static Instruction *processUMulZExtIdiom(ICmpInst &I, Value *MulVal,
-                                         const APInt *OtherVal,
-                                         InstCombinerImpl &IC) {
+static Instruction *processUZExtIdiom(ICmpInst &I, Value *Val,
+                                      const APInt *OtherVal,
+                                      InstCombinerImpl &IC) {
   // Don't bother doing this transformation for pointers, don't do it for
   // vectors.
-  if (!isa<IntegerType>(MulVal->getType()))
+  if (!isa<IntegerType>(Val->getType()))
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arsenm wrote:

I don't understand why this would skip vectors. Also the comment about pointers doesn't make sense, a pointer type couldn't reach here in the first place 

https://github.com/llvm/llvm-project/pull/140178