[llvm-commits] [llvm] r52097 - in /llvm/trunk: lib/Transforms/Scalar/InstructionCombining.cpp test/Transforms/InstCombine/2008-06-08-ICmpPHI.ll

[Chris Lattner]

Author: lattner
Date: Sun Jun  8 15:52:11 2008
New Revision: 52097

URL: http://llvm.org/viewvc/llvm-project?rev=52097&view=rev
Log:
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.

Added:
    llvm/trunk/test/Transforms/InstCombine/2008-06-08-ICmpPHI.ll
Modified:
    llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp

Modified: llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp?rev=52097&r1=52096&r2=52097&view=diff

==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp Sun Jun  8 15:52:11 2008
@@ -5043,8 +5043,12 @@
     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 @@
         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

Added: llvm/trunk/test/Transforms/InstCombine/2008-06-08-ICmpPHI.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/2008-06-08-ICmpPHI.ll?rev=52097&view=auto

==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/2008-06-08-ICmpPHI.ll (added)
+++ llvm/trunk/test/Transforms/InstCombine/2008-06-08-ICmpPHI.ll Sun Jun  8 15:52:11 2008
@@ -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(...)