From: Nick Lewycky <nicholas@mxc.ca>
Date: Thu, 4 Mar 2010 06:54:10 +0000 (+0000)
Subject: Make the 'icmp pred trunc(ext(X)), CST --> icmp pred X, ext(trunc(CST))'
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=5bf7f88ea28dae0cad4f311cc5ef708b6ce50e8f;p=oota-llvm.git

Make the 'icmp pred trunc(ext(X)), CST --> icmp pred X, ext(trunc(CST))'
transformation much more careful. Truncating binary '01' to '1' sounds like it's
safe until you realize that it switched from positive to negative under a signed
interpretation, and that depends on the icmp predicate.

Also a few miscellaneous cleanups.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@97721 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/VMCore/ConstantFold.cpp b/lib/VMCore/ConstantFold.cpp
index 47244a0e323..549977c2342 100644
--- a/lib/VMCore/ConstantFold.cpp
+++ b/lib/VMCore/ConstantFold.cpp
@@ -2070,7 +2070,7 @@ Constant *llvm::ConstantFoldCompareInstruction(unsigned short pred,
     if (ConstantExpr *CE2 = dyn_cast<ConstantExpr>(C2)) {
       Constant *CE2Op0 = CE2->getOperand(0);
       if (CE2->getOpcode() == Instruction::BitCast &&
-          CE2->getType()->isVectorTy()==CE2Op0->getType()->isVectorTy()) {
+          CE2->getType()->isVectorTy() == CE2Op0->getType()->isVectorTy()) {
         Constant *Inverse = ConstantExpr::getBitCast(C1, CE2Op0->getType());
         return ConstantExpr::getICmp(pred, Inverse, CE2Op0);
       }
@@ -2078,8 +2078,8 @@ Constant *llvm::ConstantFoldCompareInstruction(unsigned short pred,
 
     // If the left hand side is an extension, try eliminating it.
     if (ConstantExpr *CE1 = dyn_cast<ConstantExpr>(C1)) {
-      if (CE1->getOpcode() == Instruction::SExt ||
-          CE1->getOpcode() == Instruction::ZExt) {
+      if ((CE1->getOpcode() == Instruction::SExt && ICmpInst::isSigned(pred)) ||
+          (CE1->getOpcode() == Instruction::ZExt && !ICmpInst::isSigned(pred))){
         Constant *CE1Op0 = CE1->getOperand(0);
         Constant *CE1Inverse = ConstantExpr::getTrunc(CE1, CE1Op0->getType());
         if (CE1Inverse == CE1Op0) {
@@ -2097,27 +2097,8 @@ Constant *llvm::ConstantFoldCompareInstruction(unsigned short pred,
       // If C2 is a constant expr and C1 isn't, flip them around and fold the
       // other way if possible.
       // Also, if C1 is null and C2 isn't, flip them around.
-      switch (pred) {
-      case ICmpInst::ICMP_EQ:
-      case ICmpInst::ICMP_NE:
-        // No change of predicate required.
-        return ConstantExpr::getICmp(pred, C2, C1);
-
-      case ICmpInst::ICMP_ULT:
-      case ICmpInst::ICMP_SLT:
-      case ICmpInst::ICMP_UGT:
-      case ICmpInst::ICMP_SGT:
-      case ICmpInst::ICMP_ULE:
-      case ICmpInst::ICMP_SLE:
-      case ICmpInst::ICMP_UGE:
-      case ICmpInst::ICMP_SGE:
-        // Change the predicate as necessary to swap the operands.
-        pred = ICmpInst::getSwappedPredicate((ICmpInst::Predicate)pred);
-        return ConstantExpr::getICmp(pred, C2, C1);
-
-      default:  // These predicates cannot be flopped around.
-        break;
-      }
+      pred = ICmpInst::getSwappedPredicate((ICmpInst::Predicate)pred);
+      return ConstantExpr::getICmp(pred, C2, C1);
     }
   }
   return 0;
diff --git a/test/Transforms/InstCombine/2010-03-03-ExtElim.ll b/test/Transforms/InstCombine/2010-03-03-ExtElim.ll
new file mode 100644
index 00000000000..2df12d670ad
--- /dev/null
+++ b/test/Transforms/InstCombine/2010-03-03-ExtElim.ll
@@ -0,0 +1,18 @@
+; RUN: opt -instcombine -S %s | FileCheck %s
+; PR6486
+
+target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:32:32-n8:16:32"
+target triple = "i386-unknown-linux-gnu"
+
+@g_92 = common global [2 x i32*] zeroinitializer, align 4 ; <[2 x i32*]*> [#uses=1]
+@g_177 = constant i32** bitcast (i8* getelementptr (i8* bitcast ([2 x i32*]* @g_92 to i8*), i64 4) to i32**), align 4 ; <i32***> [#uses=1]
+
+define i1 @test() nounwind {
+; CHECK: @test
+  %tmp = load i32*** @g_177                       ; <i32**> [#uses=1]
+  %cmp = icmp ne i32** null, %tmp                 ; <i1> [#uses=1]
+  %conv = zext i1 %cmp to i32                     ; <i32> [#uses=1]
+  %cmp1 = icmp sle i32 0, %conv                   ; <i1> [#uses=1]
+  ret i1 %cmp1
+; CHECK: ret i1 true
+}