[llvm] r263618 - [JumpThreading] See through Cast Instructions

[Haicheng Wu via llvm-commits]

Author: haicheng
Date: Tue Mar 15 23:52:52 2016
New Revision: 263618

URL: http://llvm.org/viewvc/llvm-project?rev=263618&view=rev
Log:
[JumpThreading] See through Cast Instructions

To capture more jump-thread opportunity.

Modified:
    llvm/trunk/lib/Transforms/Scalar/JumpThreading.cpp
    llvm/trunk/test/Transforms/JumpThreading/basic.ll

Modified: llvm/trunk/lib/Transforms/Scalar/JumpThreading.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/JumpThreading.cpp?rev=263618&r1=263617&r2=263618&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/JumpThreading.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/JumpThreading.cpp Tue Mar 15 23:52:52 2016
@@ -465,6 +465,25 @@ ComputeValueKnownInPredecessors(Value *V
     return !Result.empty();
   }
 
+  // Handle Cast instructions.  Only see through Cast when the source operand is
+  // PHI or Cmp and the source type is i1 to save the compilation time.
+  if (CastInst *CI = dyn_cast<CastInst>(I)) {
+    Value *Source = CI->getOperand(0);
+    if (!Source->getType()->isIntegerTy(1))
+      return false;
+    if (!isa<PHINode>(Source) && !isa<CmpInst>(Source))
+      return false;
+    ComputeValueKnownInPredecessors(Source, BB, Result, Preference, CxtI);
+    if (Result.empty())
+      return false;
+
+    // Convert the known values.
+    for (auto &R : Result)
+      R.first = ConstantExpr::getCast(CI->getOpcode(), R.first, CI->getType());
+
+    return true;
+  }
+
   PredValueInfoTy LHSVals, RHSVals;
 
   // Handle some boolean conditions.

Modified: llvm/trunk/test/Transforms/JumpThreading/basic.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/JumpThreading/basic.ll?rev=263618&r1=263617&r2=263618&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/JumpThreading/basic.ll (original)
+++ llvm/trunk/test/Transforms/JumpThreading/basic.ll Tue Mar 15 23:52:52 2016
@@ -476,6 +476,40 @@ exit1:
 ; CHECK: }
 }
 
+;;; Verify that we can handle constraint propagation through cast.
+define i32 @test16(i1 %cond) {
+Entry:
+; CHECK-LABEL: @test16(
+	br i1 %cond, label %Merge, label %F1
+
+; CHECK: Entry:
+; CHECK-NEXT:  br i1 %cond, label %F2, label %Merge
+
+F1:
+	%v1 = call i32 @f1()
+	br label %Merge
+
+Merge:
+	%B = phi i32 [0, %Entry], [%v1, %F1]
+	%M = icmp eq i32 %B, 0 
+	%M1 = zext i1 %M to i32
+	%N = icmp eq i32 %M1, 0 
+	br i1 %N, label %T2, label %F2
+
+; CHECK: Merge:
+; CHECK-NOT: phi
+; CHECK-NEXT:   %v1 = call i32 @f1()
+
+T2:
+	%Q = call i32 @f2() 
+	ret i32 %Q
+
+F2:
+	ret i32 %B
+; CHECK: F2:
+; CHECK-NEXT: phi i32
+}
+
 ; In this test we check that block duplication is inhibited by the presence
 ; of a function with the 'noduplicate' attribute.