[llvm] r175995 - CVP: If we have a PHI with an incoming select, try to skip the select.
Benjamin Kramer
benny.kra at googlemail.com
Sun Feb 24 07:34:43 PST 2013
Author: d0k
Date: Sun Feb 24 09:34:43 2013
New Revision: 175995
URL: http://llvm.org/viewvc/llvm-project?rev=175995&view=rev
Log:
CVP: If we have a PHI with an incoming select, try to skip the select.
This is a common pattern with dyn_cast and similar constructs, when the
PHI no longer depends on the select it can often be turned into a simpler
construct or even get hoisted out of the loop.
PR15340.
Modified:
llvm/trunk/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp
llvm/trunk/test/Transforms/CorrelatedValuePropagation/basic.ll
Modified: llvm/trunk/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp?rev=175995&r1=175994&r2=175995&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp Sun Feb 24 09:34:43 2013
@@ -21,6 +21,8 @@
#include "llvm/IR/Instructions.h"
#include "llvm/Pass.h"
#include "llvm/Support/CFG.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/Utils/Local.h"
using namespace llvm;
@@ -97,12 +99,29 @@ bool CorrelatedValuePropagation::process
Value *Incoming = P->getIncomingValue(i);
if (isa<Constant>(Incoming)) continue;
- Constant *C = LVI->getConstantOnEdge(P->getIncomingValue(i),
- P->getIncomingBlock(i),
- BB);
- if (!C) continue;
+ Value *V = LVI->getConstantOnEdge(Incoming, P->getIncomingBlock(i), BB);
- P->setIncomingValue(i, C);
+ // Look if the incoming value is a select with a constant but LVI tells us
+ // that the incoming value can never be that constant. In that case replace
+ // the incoming value with the other value of the select. This often allows
+ // us to remove the select later.
+ if (!V) {
+ SelectInst *SI = dyn_cast<SelectInst>(Incoming);
+ if (!SI) continue;
+
+ Constant *C = dyn_cast<Constant>(SI->getFalseValue());
+ if (!C) continue;
+
+ if (LVI->getPredicateOnEdge(ICmpInst::ICMP_EQ, SI, C,
+ P->getIncomingBlock(i), BB) !=
+ LazyValueInfo::False)
+ continue;
+
+ DEBUG(dbgs() << "CVP: Threading PHI over " << *SI << '\n');
+ V = SI->getTrueValue();
+ }
+
+ P->setIncomingValue(i, V);
Changed = true;
}
Modified: llvm/trunk/test/Transforms/CorrelatedValuePropagation/basic.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/CorrelatedValuePropagation/basic.ll?rev=175995&r1=175994&r2=175995&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/CorrelatedValuePropagation/basic.ll (original)
+++ llvm/trunk/test/Transforms/CorrelatedValuePropagation/basic.ll Sun Feb 24 09:34:43 2013
@@ -81,6 +81,26 @@ LessThanOrEqualToTwo:
ret i32 0
}
+declare i32* @f(i32*)
+define void @test5(i32* %x, i32* %y) {
+; CHECK: @test5
+entry:
+ %pre = icmp eq i32* %x, null
+ br i1 %pre, label %return, label %loop
+
+loop:
+ %phi = phi i32* [ %sel, %loop ], [ %x, %entry ]
+; CHECK: %phi = phi i32* [ %f, %loop ], [ %x, %entry ]
+ %f = tail call i32* @f(i32* %phi)
+ %cmp1 = icmp ne i32* %f, %y
+ %sel = select i1 %cmp1, i32* %f, i32* null
+ %cmp2 = icmp eq i32* %sel, null
+ br i1 %cmp2, label %return, label %loop
+
+return:
+ ret void
+}
+
define i32 @switch1(i32 %s) {
; CHECK: @switch1
entry:
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