[PATCH] D24677: [InstCombine] allow vector types for constant folding / computeKnownBits (PR24942)

[Sanjay Patel via llvm-commits]

spatel created this revision.
spatel added reviewers: arsenm, majnemer, efriedma.
spatel added a subscriber: llvm-commits.
Herald added subscribers: wdng, mcrosier.

computeKnownBits() already works for integer vectors, so allow vector types when calling that from InstCombine.

I don't think the change to use m_APInt is strictly necessary in computeKnownBits because we do check for ConstantVector later, but it's more efficient to handle the splat case without needing to loop on vector elements.

This should work with InstSimplify, but doesn't yet, so I made that a FIXME comment on the test for PR24942:
https://llvm.org/bugs/show_bug.cgi?id=24942

https://reviews.llvm.org/D24677

Files:
  lib/Analysis/ValueTracking.cpp
  lib/Transforms/InstCombine/InstructionCombining.cpp
  test/Transforms/InstCombine/and.ll
  test/Transforms/InstCombine/trunc.ll

Index: test/Transforms/InstCombine/trunc.ll
===================================================================
--- test/Transforms/InstCombine/trunc.ll
+++ test/Transforms/InstCombine/trunc.ll
@@ -437,20 +437,16 @@
 
 define <8 x i16> @trunc_shl_v8i16_v8i32_16(<8 x i32> %a) {
 ; CHECK-LABEL: @trunc_shl_v8i16_v8i32_16(
-; CHECK-NEXT:    [[SHL:%.*]] = shl <8 x i32> %a, <i32 16, i32 16, i32 16, i32 16, i32 16, i32 16, i32 16, i32 16>
-; CHECK-NEXT:    [[CONV:%.*]] = trunc <8 x i32> [[SHL]] to <8 x i16>
-; CHECK-NEXT:    ret <8 x i16> [[CONV]]
+; CHECK-NEXT:    ret <8 x i16> zeroinitializer
 ;
   %shl = shl <8 x i32> %a, <i32 16, i32 16, i32 16, i32 16, i32 16, i32 16, i32 16, i32 16>
   %conv = trunc <8 x i32> %shl to <8 x i16>
   ret <8 x i16> %conv
 }
 
 define <8 x i16> @trunc_shl_v8i16_v8i32_17(<8 x i32> %a) {
 ; CHECK-LABEL: @trunc_shl_v8i16_v8i32_17(
-; CHECK-NEXT:    [[SHL:%.*]] = shl <8 x i32> %a, <i32 17, i32 17, i32 17, i32 17, i32 17, i32 17, i32 17, i32 17>
-; CHECK-NEXT:    [[CONV:%.*]] = trunc <8 x i32> [[SHL]] to <8 x i16>
-; CHECK-NEXT:    ret <8 x i16> [[CONV]]
+; CHECK-NEXT:    ret <8 x i16> zeroinitializer
 ;
   %shl = shl <8 x i32> %a, <i32 17, i32 17, i32 17, i32 17, i32 17, i32 17, i32 17, i32 17>
   %conv = trunc <8 x i32> %shl to <8 x i16>
Index: test/Transforms/InstCombine/and.ll
===================================================================
--- test/Transforms/InstCombine/and.ll
+++ test/Transforms/InstCombine/and.ll
@@ -414,3 +414,14 @@
   ret i32 %tmp.4
 }
 
+; FIXME: This test should only need -instsimplify (ValueTracking / computeKnownBits), not -instcombine.
+
+define <2 x i32> @PR24942(<2 x i32> %x) {
+; CHECK-LABEL: @PR24942(
+; CHECK-NEXT:    ret <2 x i32> zeroinitializer
+;
+  %lshr = lshr <2 x i32> %x, <i32 31, i32 31>
+  %and = and <2 x i32> %lshr, <i32 2, i32 2>
+  ret <2 x i32> %and
+}
+
Index: lib/Transforms/InstCombine/InstructionCombining.cpp
===================================================================
--- lib/Transforms/InstCombine/InstructionCombining.cpp
+++ lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -2859,13 +2859,14 @@
 
     // In general, it is possible for computeKnownBits to determine all bits in
     // a value even when the operands are not all constants.
-    if (ExpensiveCombines && !I->use_empty() && I->getType()->isIntegerTy()) {
-      unsigned BitWidth = I->getType()->getScalarSizeInBits();
+    Type *Ty = I->getType();
+    if (ExpensiveCombines && !I->use_empty() && Ty->isIntOrIntVectorTy()) {
+      unsigned BitWidth = Ty->getScalarSizeInBits();
       APInt KnownZero(BitWidth, 0);
       APInt KnownOne(BitWidth, 0);
       computeKnownBits(I, KnownZero, KnownOne, /*Depth*/0, I);
       if ((KnownZero | KnownOne).isAllOnesValue()) {
-        Constant *C = ConstantInt::get(I->getContext(), KnownOne);
+        Constant *C = ConstantInt::get(Ty, KnownOne);
         DEBUG(dbgs() << "IC: ConstFold (all bits known) to: " << *C <<
                         " from: " << *I << '\n');
 
Index: lib/Analysis/ValueTracking.cpp
===================================================================
--- lib/Analysis/ValueTracking.cpp
+++ lib/Analysis/ValueTracking.cpp
@@ -1451,9 +1451,10 @@
          KnownOne.getBitWidth() == BitWidth &&
          "V, KnownOne and KnownZero should have same BitWidth");
 
-  if (const ConstantInt *CI = dyn_cast<ConstantInt>(V)) {
-    // We know all of the bits for a constant!
-    KnownOne = CI->getValue();
+  const APInt *C;
+  if (match(V, m_APInt(C))) {
+    // We know all of the bits for a scalar constant or a splat vector constant!
+    KnownOne = *C;
     KnownZero = ~KnownOne;
     return;
   }


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