[llvm-branch-commits] [llvm] InstCombine: Implement SimplifyDemandedFPClass for frexp (PR #176122)

[Yingwei Zheng via llvm-branch-commits]

================
@@ -2941,6 +2941,55 @@ Value *InstCombinerImpl::SimplifyDemandedUseFPClass(Instruction *I,
     Known = KnownLHS | KnownRHS;
     break;
   }
+  case Instruction::ExtractValue: {
+    ExtractValueInst *Extract = cast<ExtractValueInst>(I);
+    ArrayRef<unsigned> Indices = Extract->getIndices();
+    Value *Src = Extract->getAggregateOperand();
+    if (isa<StructType>(Src->getType()) && Indices.size() == 1 &&
+        Indices[0] == 0) {
+      if (auto *II = dyn_cast<IntrinsicInst>(Src)) {
+        switch (II->getIntrinsicID()) {
+        case Intrinsic::frexp: {
+          FPClassTest SrcDemandedMask = fcNone;
+          if (DemandedMask & fcNan)
+            SrcDemandedMask |= fcNan;
+          if (DemandedMask & fcNegFinite)
+            SrcDemandedMask |= fcNegFinite;
+          if (DemandedMask & fcPosFinite)
+            SrcDemandedMask |= fcPosFinite;
+          if (DemandedMask & fcPosInf)
+            SrcDemandedMask |= fcPosInf;
+          if (DemandedMask & fcNegInf)
+            SrcDemandedMask |= fcNegInf;
+
+          KnownFPClass KnownSrc;
+          if (SimplifyDemandedFPClass(II, 0, SrcDemandedMask, KnownSrc,
----------------
dtcxzyw wrote:

The latter one. Alive2: https://alive2.llvm.org/ce/z/y2ibWd
```
Transformation doesn't verify!

ERROR: Mismatch in memory

Example:
i1 %cond = #x0 (0)
half %unknown = #x7c21 (SNaN)
ptr %ptr = pointer(non-local, block_id=1, offset=0) / Address=#x08

Source:
half %select = #x7c00 (+oo)
{half, i16, i32} %frexp = { #x7c00 (+oo), poison, #x00000003 (3) }
half %frexp.mant = #x7c00 (+oo)
half %frexp.mant2 = #x7c00 (+oo)

SOURCE MEMORY STATE
===================
NON-LOCAL BLOCKS:
Block 0 >       size: 0 align: 2        alloc type: 0   alive: false    address: #x00
Block 1 >       size: 5 align: 1        alloc type: 0   alive: true     address: #x08
Contents:
*: #x0000


Target:
{half, i16, i32} %frexp = { #x7c21 (SNaN), poison, #x00000003 (3) }
half %frexp.mant = #x7c21 (SNaN)
half %frexp.mant2 = #x7c21 (SNaN)

TARGET MEMORY STATE
===================
NON-LOCAL BLOCKS:
Block 0 >       size: 0 align: 2        alloc type: 0   alive: false    address: #x00
Block 1 >       size: 5 align: 1        alloc type: 0   alive: true     address: #x08
Contents:
*: #x0000


Mismatch in pointer(non-local, block_id=1, offset=0)
Source value: #x7c00
Target value: #x7c21
```
The counterexample provided by Alive2 is not good enough (the return value of src is poison).


https://github.com/llvm/llvm-project/pull/176122