[CodeGenPrepare][RISCV] Correct the MathUsed flag for shouldFormOverflowOp

For add, if we match the constant edge case the add isn't used by
the compare so we shouldn't check for 2 users.

For sub, the compare is not a user of the sub so the math is
used if the sub has any users.

This regresses RISC-V which I will work on other patches for.

Reviewed By: RKSimon

Differential Revision: https://reviews.llvm.org/D146786

1 files changed, 4 insertions, 2 deletions

diff --git a/llvm/lib/CodeGen/CodeGenPrepare.cpp b/llvm/lib/CodeGen/CodeGenPrepare.cpp
index b571b5a..16196b0 100644
--- a/llvm/lib/CodeGen/CodeGenPrepare.cpp
+++ b/llvm/lib/CodeGen/CodeGenPrepare.cpp
@@ -1579,6 +1579,7 @@ static bool matchUAddWithOverflowConstantEdgeCases(CmpInst *Cmp,
 /// intrinsic. Return true if any changes were made.
 bool CodeGenPrepare::combineToUAddWithOverflow(CmpInst *Cmp,
                                                ModifyDT &ModifiedDT) {
+  bool EdgeCase = false;
   Value *A, *B;
   BinaryOperator *Add;
   if (!match(Cmp, m_UAddWithOverflow(m_Value(A), m_Value(B), m_BinOp(Add)))) {
@@ -1587,11 +1588,12 @@ bool CodeGenPrepare::combineToUAddWithOverflow(CmpInst *Cmp,
     // Set A and B in case we match matchUAddWithOverflowConstantEdgeCases.
     A = Add->getOperand(0);
     B = Add->getOperand(1);
+    EdgeCase = true;
   }
 
   if (!TLI->shouldFormOverflowOp(ISD::UADDO,
                                  TLI->getValueType(*DL, Add->getType()),
-                                 Add->hasNUsesOrMore(2)))
+                                 Add->hasNUsesOrMore(EdgeCase ? 1 : 2)))
     return false;
 
   // We don't want to move around uses of condition values this late, so we
@@ -1660,7 +1662,7 @@ bool CodeGenPrepare::combineToUSubWithOverflow(CmpInst *Cmp,
 
   if (!TLI->shouldFormOverflowOp(ISD::USUBO,
                                  TLI->getValueType(*DL, Sub->getType()),
-                                 Sub->hasNUsesOrMore(2)))
+                                 Sub->hasNUsesOrMore(1)))
     return false;
 
   if (!replaceMathCmpWithIntrinsic(Sub, Sub->getOperand(0), Sub->getOperand(1),