From: Dan Gohman <gohman@apple.com>
Date: Fri, 1 Jul 2011 01:03:43 +0000 (+0000)
Subject: Improve constant folding of undef for cmp and select operators.
X-Git-Url: http://plrg.eecs.uci.edu/git/?a=commitdiff_plain;h=68c0dbc14fb7599987fb3e27be4e12c1ac36535e;p=oota-llvm.git

Improve constant folding of undef for cmp and select operators.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@134223 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Analysis/InstructionSimplify.cpp b/lib/Analysis/InstructionSimplify.cpp
index 9d78f8bf404..8709f6bf9d2 100644
--- a/lib/Analysis/InstructionSimplify.cpp
+++ b/lib/Analysis/InstructionSimplify.cpp
@@ -2204,15 +2204,15 @@ Value *llvm::SimplifySelectInst(Value *CondVal, Value *TrueVal, Value *FalseVal,
   if (TrueVal == FalseVal)
     return TrueVal;
 
-  if (isa<UndefValue>(TrueVal))   // select C, undef, X -> X
-    return FalseVal;
-  if (isa<UndefValue>(FalseVal))   // select C, X, undef -> X
-    return TrueVal;
   if (isa<UndefValue>(CondVal)) {  // select undef, X, Y -> X or Y
     if (isa<Constant>(TrueVal))
       return TrueVal;
     return FalseVal;
   }
+  if (isa<UndefValue>(TrueVal))   // select C, undef, X -> X
+    return FalseVal;
+  if (isa<UndefValue>(FalseVal))   // select C, X, undef -> X
+    return TrueVal;
 
   return 0;
 }
diff --git a/lib/VMCore/ConstantFold.cpp b/lib/VMCore/ConstantFold.cpp
index 8cca06fdda0..b7a1350ff5a 100644
--- a/lib/VMCore/ConstantFold.cpp
+++ b/lib/VMCore/ConstantFold.cpp
@@ -730,9 +730,12 @@ Constant *llvm::ConstantFoldSelectInstruction(Constant *Cond,
   }
 
 
+  if (isa<UndefValue>(Cond)) {
+    if (isa<UndefValue>(V1)) return V1;
+    return V2;
+  }
   if (isa<UndefValue>(V1)) return V2;
   if (isa<UndefValue>(V2)) return V1;
-  if (isa<UndefValue>(Cond)) return V1;
   if (V1 == V2) return V1;
 
   if (ConstantExpr *TrueVal = dyn_cast<ConstantExpr>(V1)) {
@@ -1851,7 +1854,9 @@ Constant *llvm::ConstantFoldCompareInstruction(unsigned short pred,
   if (isa<UndefValue>(C1) || isa<UndefValue>(C2)) {
     // For EQ and NE, we can always pick a value for the undef to make the
     // predicate pass or fail, so we can return undef.
-    if (ICmpInst::isEquality(ICmpInst::Predicate(pred)))
+    // Also, if both operands are undef, we can return undef.
+    if (ICmpInst::isEquality(ICmpInst::Predicate(pred)) ||
+        (isa<UndefValue>(C1) && isa<UndefValue>(C2)))
       return UndefValue::get(ResultTy);
     // Otherwise, pick the same value as the non-undef operand, and fold
     // it to true or false.
diff --git a/test/Transforms/InstSimplify/binop.ll b/test/Transforms/InstSimplify/binop.ll
deleted file mode 100644
index f4bc55753a5..00000000000
--- a/test/Transforms/InstSimplify/binop.ll
+++ /dev/null
@@ -1,99 +0,0 @@
-; RUN: opt -instsimplify -S < %s | FileCheck %s
-
-; @test0
-; CHECK: ret i64 undef
-define i64 @test0() {
-  %r = mul i64 undef, undef
-  ret i64 %r
-}
-
-; @test1
-; CHECK: ret i64 undef
-define i64 @test1() {
-  %r = mul i64 3, undef
-  ret i64 %r
-}
-
-; @test2
-; CHECK: ret i64 undef
-define i64 @test2() {
-  %r = mul i64 undef, 3
-  ret i64 %r
-}
-
-; @test3
-; CHECK: ret i64 0
-define i64 @test3() {
-  %r = mul i64 undef, 6
-  ret i64 %r
-}
-
-; @test4
-; CHECK: ret i64 0
-define i64 @test4() {
-  %r = mul i64 6, undef
-  ret i64 %r
-}
-
-; @test5
-; CHECK: ret i64 undef
-define i64 @test5() {
-  %r = and i64 undef, undef
-  ret i64 %r
-}
-
-; @test6
-; CHECK: ret i64 undef
-define i64 @test6() {
-  %r = or i64 undef, undef
-  ret i64 %r
-}
-
-; @test7
-; CHECK: ret i64 undef
-define i64 @test7() {
-  %r = udiv i64 undef, 1
-  ret i64 %r
-}
-
-; @test8
-; CHECK: ret i64 undef
-define i64 @test8() {
-  %r = sdiv i64 undef, 1
-  ret i64 %r
-}
-
-; @test9
-; CHECK: ret i64 0
-define i64 @test9() {
-  %r = urem i64 undef, 1
-  ret i64 %r
-}
-
-; @test10
-; CHECK: ret i64 0
-define i64 @test10() {
-  %r = srem i64 undef, 1
-  ret i64 %r
-}
-
-; @test11
-; CHECK: ret i64 undef
-define i64 @test11() {
-  %r = shl i64 undef, undef
-  ret i64 %r
-}
-
-; @test12
-; CHECK: ret i64 undef
-define i64 @test12() {
-  %r = ashr i64 undef, undef
-  ret i64 %r
-}
-
-; @test13
-; CHECK: ret i64 undef
-define i64 @test13() {
-  %r = lshr i64 undef, undef
-  ret i64 %r
-}
diff --git a/test/Transforms/InstSimplify/undef.ll b/test/Transforms/InstSimplify/undef.ll
new file mode 100644
index 00000000000..8134cc84874
--- /dev/null
+++ b/test/Transforms/InstSimplify/undef.ll
@@ -0,0 +1,127 @@
+; RUN: opt -instsimplify -S < %s | FileCheck %s
+
+; @test0
+; CHECK: ret i64 undef
+define i64 @test0() {
+  %r = mul i64 undef, undef
+  ret i64 %r
+}
+
+; @test1
+; CHECK: ret i64 undef
+define i64 @test1() {
+  %r = mul i64 3, undef
+  ret i64 %r
+}
+
+; @test2
+; CHECK: ret i64 undef
+define i64 @test2() {
+  %r = mul i64 undef, 3
+  ret i64 %r
+}
+
+; @test3
+; CHECK: ret i64 0
+define i64 @test3() {
+  %r = mul i64 undef, 6
+  ret i64 %r
+}
+
+; @test4
+; CHECK: ret i64 0
+define i64 @test4() {
+  %r = mul i64 6, undef
+  ret i64 %r
+}
+
+; @test5
+; CHECK: ret i64 undef
+define i64 @test5() {
+  %r = and i64 undef, undef
+  ret i64 %r
+}
+
+; @test6
+; CHECK: ret i64 undef
+define i64 @test6() {
+  %r = or i64 undef, undef
+  ret i64 %r
+}
+
+; @test7
+; CHECK: ret i64 undef
+define i64 @test7() {
+  %r = udiv i64 undef, 1
+  ret i64 %r
+}
+
+; @test8
+; CHECK: ret i64 undef
+define i64 @test8() {
+  %r = sdiv i64 undef, 1
+  ret i64 %r
+}
+
+; @test9
+; CHECK: ret i64 0
+define i64 @test9() {
+  %r = urem i64 undef, 1
+  ret i64 %r
+}
+
+; @test10
+; CHECK: ret i64 0
+define i64 @test10() {
+  %r = srem i64 undef, 1
+  ret i64 %r
+}
+
+; @test11
+; CHECK: ret i64 undef
+define i64 @test11() {
+  %r = shl i64 undef, undef
+  ret i64 %r
+}
+
+; @test12
+; CHECK: ret i64 undef
+define i64 @test12() {
+  %r = ashr i64 undef, undef
+  ret i64 %r
+}
+
+; @test13
+; CHECK: ret i64 undef
+define i64 @test13() {
+  %r = lshr i64 undef, undef
+  ret i64 %r
+}
+
+; @test14
+; CHECK: ret i1 undef
+define i1 @test14() {
+  %r = icmp slt i64 undef, undef
+  ret i1 %r
+}
+
+; @test15
+; CHECK: ret i1 undef
+define i1 @test15() {
+  %r = icmp ult i64 undef, undef
+  ret i1 %r
+}
+
+; @test16
+; CHECK: ret i64 undef
+define i64 @test16(i64 %a) {
+  %r = select i1 undef, i64 %a, i64 undef
+  ret i64 %r
+}
+
+; @test17
+; CHECK: ret i64 undef
+define i64 @test17(i64 %a) {
+  %r = select i1 undef, i64 undef, i64 %a
+  ret i64 %r
+}