Limit the icmp+phi merging optimization to the cases where it is profitable:

don't make i1 phis when it won't be possible to eliminate them.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@52097 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/Scalar/InstructionCombining.cpp b/lib/Transforms/Scalar/InstructionCombining.cpp
index 67c40fe21c9fae77bc07808c60755e256fac26bc..3b181c85d261afff70c01891efa38f72b1c44ff9 100644 (file)
--- a/lib/Transforms/Scalar/InstructionCombining.cpp
+++ b/lib/Transforms/Scalar/InstructionCombining.cpp
@@ -5043,8 +5043,12 @@ Instruction *InstCombiner::visitFCmpInst(FCmpInst &I) {
     if (Instruction *LHSI = dyn_cast<Instruction>(Op0))
       switch (LHSI->getOpcode()) {
       case Instruction::PHI:
-        if (Instruction *NV = FoldOpIntoPhi(I))
-          return NV;
+        // Only fold fcmp into the PHI if the phi and fcmp are in the same
+        // block.  If in the same block, we're encouraging jump threading.  If
+        // not, we are just pessimizing the code by making an i1 phi.
+        if (LHSI->getParent() == I.getParent())
+          if (Instruction *NV = FoldOpIntoPhi(I))
+            return NV;
         break;
       case Instruction::SIToFP:
       case Instruction::UIToFP:
@@ -5348,8 +5352,12 @@ Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
         break;
 
       case Instruction::PHI:
-        if (Instruction *NV = FoldOpIntoPhi(I))
-          return NV;
+        // Only fold icmp into the PHI if the phi and fcmp are in the same
+        // block.  If in the same block, we're encouraging jump threading.  If
+        // not, we are just pessimizing the code by making an i1 phi.
+        if (LHSI->getParent() == I.getParent())
+          if (Instruction *NV = FoldOpIntoPhi(I))
+            return NV;
         break;
       case Instruction::Select: {
         // If either operand of the select is a constant, we can fold the

diff --git a/test/Transforms/InstCombine/2008-06-08-ICmpPHI.ll b/test/Transforms/InstCombine/2008-06-08-ICmpPHI.ll
new file mode 100644 (file)
index 0000000..555f810
--- /dev/null
+++ b/test/Transforms/InstCombine/2008-06-08-ICmpPHI.ll
@@ -0,0 +1,49 @@
+; RUN: llvm-as < %s | opt -instcombine | llvm-dis | grep {phi i32} | count 2
+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-f80:128:128"
+target triple = "i386-apple-darwin8"
+
+define void @test() nounwind  {
+entry:
+       br label %bb
+
+bb:            ; preds = %bb16, %entry
+       %i.0 = phi i32 [ 0, %entry ], [ %indvar.next, %somebb ]         ; <i32> [#uses=1]
+       %x.0 = phi i32 [ 37, %entry ], [ %tmp17, %somebb ]              ; <i32> [#uses=1]
+       %tmp = tail call i32 (...)* @bork( ) nounwind           ; <i32> [#uses=0]
+       %tmp1 = tail call i32 (...)* @bork( ) nounwind          ; <i32> [#uses=0]
+       %tmp2 = tail call i32 (...)* @bork( ) nounwind          ; <i32> [#uses=1]
+       %tmp3 = icmp eq i32 %tmp2, 0            ; <i1> [#uses=1]
+       br i1 %tmp3, label %bb7, label %bb5
+
+bb5:           ; preds = %bb
+       %tmp6 = tail call i32 (...)* @bork( ) nounwind          ; <i32> [#uses=0]
+       br label %bb7
+
+bb7:           ; preds = %bb5, %bb
+       %tmp8 = tail call i32 (...)* @bork( ) nounwind          ; <i32> [#uses=0]
+       %tmp9 = tail call i32 (...)* @bork( ) nounwind          ; <i32> [#uses=0]
+       %tmp11 = icmp eq i32 %x.0, 37           ; <i1> [#uses=1]
+       br i1 %tmp11, label %bb14, label %bb16
+
+bb14:          ; preds = %bb7
+       %tmp15 = tail call i32 (...)* @bar( ) nounwind          ; <i32> [#uses=0]
+       br label %bb16
+
+bb16:          ; preds = %bb14, %bb7
+       %tmp17 = tail call i32 (...)* @zap( ) nounwind          ; <i32> [#uses=1]
+       %indvar.next = add i32 %i.0, 1          ; <i32> [#uses=2]
+       %exitcond = icmp eq i32 %indvar.next, 42                ; <i1> [#uses=1]
+       br i1 %exitcond, label %return, label %somebb
+
+somebb:
+       br label %bb
+
+return:                ; preds = %bb16
+       ret void
+}
+
+declare i32 @bork(...)
+
+declare i32 @bar(...)
+
+declare i32 @zap(...)