[llvm] r314741 - [InstSimplify] teach SimplifySelectInst() to fold more vector selects

[Haicheng Wu via llvm-commits]

Author: haicheng
Date: Mon Oct  2 16:43:52 2017
New Revision: 314741

URL: http://llvm.org/viewvc/llvm-project?rev=314741&view=rev
Log:
[InstSimplify] teach SimplifySelectInst() to fold more vector selects

Call ConstantFoldSelectInstruction() to fold cases like below

select <2 x i1><i1 true, i1 false>, <2 x i8> <i8 0, i8 1>, <2 x i8> <i8 2, i8 3>

All operands are constants and the condition has mixed true and false conditions.

Differential Revision: https://reviews.llvm.org/D38369

Modified:
    llvm/trunk/include/llvm/Analysis/ConstantFolding.h
    llvm/trunk/lib/Analysis/InstructionSimplify.cpp
    llvm/trunk/test/Transforms/InstSimplify/select.ll

Modified: llvm/trunk/include/llvm/Analysis/ConstantFolding.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Analysis/ConstantFolding.h?rev=314741&r1=314740&r2=314741&view=diff
==============================================================================
--- llvm/trunk/include/llvm/Analysis/ConstantFolding.h (original)
+++ llvm/trunk/include/llvm/Analysis/ConstantFolding.h Mon Oct  2 16:43:52 2017
@@ -79,6 +79,12 @@ ConstantFoldCompareInstOperands(unsigned
 Constant *ConstantFoldBinaryOpOperands(unsigned Opcode, Constant *LHS,
                                        Constant *RHS, const DataLayout &DL);
 
+/// \brief Attempt to constant fold a select instruction with the specified
+/// operands. The constant result is returned if successful; if not, null is
+/// returned.
+Constant *ConstantFoldSelectInstruction(Constant *Cond, Constant *V1,
+                                        Constant *V2);
+
 /// \brief Attempt to constant fold a cast with the specified operand.  If it
 /// fails, it returns a constant expression of the specified operand.
 Constant *ConstantFoldCastOperand(unsigned Opcode, Constant *C, Type *DestTy,

Modified: llvm/trunk/lib/Analysis/InstructionSimplify.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/InstructionSimplify.cpp?rev=314741&r1=314740&r2=314741&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/InstructionSimplify.cpp (original)
+++ llvm/trunk/lib/Analysis/InstructionSimplify.cpp Mon Oct  2 16:43:52 2017
@@ -3580,6 +3580,9 @@ static Value *SimplifySelectInst(Value *
   // select true, X, Y  -> X
   // select false, X, Y -> Y
   if (Constant *CB = dyn_cast<Constant>(CondVal)) {
+    if (Constant *CT = dyn_cast<Constant>(TrueVal))
+      if (Constant *CF = dyn_cast<Constant>(FalseVal))
+        return ConstantFoldSelectInstruction(CB, CT, CF);
     if (CB->isAllOnesValue())
       return TrueVal;
     if (CB->isNullValue())

Modified: llvm/trunk/test/Transforms/InstSimplify/select.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstSimplify/select.ll?rev=314741&r1=314740&r2=314741&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstSimplify/select.ll (original)
+++ llvm/trunk/test/Transforms/InstSimplify/select.ll Mon Oct  2 16:43:52 2017
@@ -17,6 +17,14 @@ define <2 x i8> @vsel_fvec(<2 x i8> %x,
   ret <2 x i8> %s
 }
 
+define <2 x i8> @vsel_mixedvec() {
+; CHECK-LABEL: @vsel_mixedvec(
+; CHECK-NEXT:    ret <2 x i8> <i8 0, i8 3>
+;
+  %s = select <2 x i1><i1 true, i1 false>, <2 x i8> <i8 0, i8 1>, <2 x i8> <i8 2, i8 3>
+  ret <2 x i8> %s
+}
+
 define i32 @test1(i32 %x) {
 ; CHECK-LABEL: @test1(
 ; CHECK-NEXT:    ret i32 %x