[llvm] [AMDGPU][AggressiveInstCombine] Narrow 64 bit math to 32 bit if profitable (PR #130577)

[Yingwei Zheng via llvm-commits]

================
@@ -1224,6 +1224,68 @@ static bool foldLibCalls(Instruction &I, TargetTransformInfo &TTI,
   return false;
 }
 
+static bool tryNarrowMathIfNoOverflow(Instruction &I, TargetTransformInfo &TTI,
+                                      const DataLayout &DL) {
+  unsigned opc = I.getOpcode();
+  Type *OldType = I.getType();
+  if (opc != Instruction::Add && opc != Instruction::Mul &&
+      !OldType->isIntOrIntVectorTy()) {
+    return false;
+  }
+  unsigned OrigBit = OldType->getScalarSizeInBits();
+  unsigned MaxBitsNeed = OrigBit;
+  switch (opc) {
+  case Instruction::Add:
+    MaxBitsNeed = KnownBits::add(computeKnownBits(I.getOperand(0), DL),
+                                 computeKnownBits(I.getOperand(1), DL))
+                      .countMaxActiveBits();
+    break;
+  case Instruction::Mul:
+    MaxBitsNeed = KnownBits::mul(computeKnownBits(I.getOperand(0), DL),
+                                 computeKnownBits(I.getOperand(1), DL))
+                      .countMaxActiveBits();
+    break;
+  default:
+    break;
+  }
+
+  MaxBitsNeed = std::max<unsigned>(bit_ceil(MaxBitsNeed), 8);
+
+  if (OrigBit <= MaxBitsNeed) {
+    return false;
+  }
----------------
dtcxzyw wrote:

```suggestion
  if (OrigBit <= MaxBitsNeed)
    return false;
```

https://github.com/llvm/llvm-project/pull/130577