[llvm] r181037 - LoopVectorizer: Add support for if-conversion of PHINodes with 3+ incoming values.
Nadav Rotem
nrotem at apple.com
Fri May 3 10:42:56 PDT 2013
Author: nadav
Date: Fri May 3 12:42:55 2013
New Revision: 181037
URL: http://llvm.org/viewvc/llvm-project?rev=181037&view=rev
Log:
LoopVectorizer: Add support for if-conversion of PHINodes with 3+ incoming values.
By supporting the vectorization of PHINodes with more than two incoming values we can increase the complexity of nested if statements.
We can now vectorize this loop:
int foo(int *A, int *B, int n) {
for (int i=0; i < n; i++) {
int x = 9;
if (A[i] > B[i]) {
if (A[i] > 19) {
x = 3;
} else if (B[i] < 4 ) {
x = 4;
} else {
x = 5;
}
}
A[i] = x;
}
}
Added:
llvm/trunk/test/Transforms/LoopVectorize/if-conversion-nest.ll
Modified:
llvm/trunk/lib/Transforms/Vectorize/LoopVectorize.cpp
Modified: llvm/trunk/lib/Transforms/Vectorize/LoopVectorize.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Vectorize/LoopVectorize.cpp?rev=181037&r1=181036&r2=181037&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Vectorize/LoopVectorize.cpp (original)
+++ llvm/trunk/lib/Transforms/Vectorize/LoopVectorize.cpp Fri May 3 12:42:55 2013
@@ -1982,18 +1982,33 @@ InnerLoopVectorizer::vectorizeBlockInLoo
// We know that all PHIs in non header blocks are converted into
// selects, so we don't have to worry about the insertion order and we
// can just use the builder.
-
// At this point we generate the predication tree. There may be
// duplications since this is a simple recursive scan, but future
// optimizations will clean it up.
- VectorParts Cond = createEdgeMask(P->getIncomingBlock(0),
- P->getParent());
- for (unsigned part = 0; part < UF; ++part) {
- VectorParts &In0 = getVectorValue(P->getIncomingValue(0));
- VectorParts &In1 = getVectorValue(P->getIncomingValue(1));
- Entry[part] = Builder.CreateSelect(Cond[part], In0[part], In1[part],
- "predphi");
+ unsigned NumIncoming = P->getNumIncomingValues();
+ assert(NumIncoming > 1 && "Invalid PHI");
+
+ // Generate a sequence of selects of the form:
+ // SELECT(Mask3, In3,
+ // SELECT(Mask2, In2,
+ // ( ...)))
+ for (unsigned In = 0; In < NumIncoming; In++) {
+ VectorParts Cond = createEdgeMask(P->getIncomingBlock(In),
+ P->getParent());
+ VectorParts &In0 = getVectorValue(P->getIncomingValue(In));
+
+ for (unsigned part = 0; part < UF; ++part) {
+ // We don't need to 'select' the first PHI operand because it is
+ // the default value if all of the other masks don't match.
+ if (In == 0)
+ Entry[part] = In0[part];
+ else
+ // Select between the current value and the previous incoming edge
+ // based on the incoming mask.
+ Entry[part] = Builder.CreateSelect(Cond[part], In0[part],
+ Entry[part], "predphi");
+ }
}
continue;
}
@@ -2273,12 +2288,6 @@ bool LoopVectorizationLegality::canVecto
if (!isa<BranchInst>(BB->getTerminator()))
return false;
- // We must have at most two predecessors because we need to convert
- // all PHIs to selects.
- unsigned Preds = std::distance(pred_begin(BB), pred_end(BB));
- if (Preds > 2)
- return false;
-
// We must be able to predicate all blocks that need to be predicated.
if (blockNeedsPredication(BB) && !blockCanBePredicated(BB))
return false;
@@ -2376,12 +2385,6 @@ bool LoopVectorizationLegality::canVecto
++it) {
if (PHINode *Phi = dyn_cast<PHINode>(it)) {
- // This should not happen because the loop should be normalized.
- if (Phi->getNumIncomingValues() != 2) {
- DEBUG(dbgs() << "LV: Found an invalid PHI.\n");
- return false;
- }
-
// Check that this PHI type is allowed.
if (!Phi->getType()->isIntegerTy() &&
!Phi->getType()->isFloatingPointTy() &&
@@ -2396,6 +2399,12 @@ bool LoopVectorizationLegality::canVecto
if (*bb != Header)
continue;
+ // We only allow if-converted PHIs with more than two incoming values.
+ if (Phi->getNumIncomingValues() != 2) {
+ DEBUG(dbgs() << "LV: Found an invalid PHI.\n");
+ return false;
+ }
+
// This is the value coming from the preheader.
Value *StartValue = Phi->getIncomingValueForBlock(PreHeader);
// Check if this is an induction variable.
Added: llvm/trunk/test/Transforms/LoopVectorize/if-conversion-nest.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LoopVectorize/if-conversion-nest.ll?rev=181037&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/LoopVectorize/if-conversion-nest.ll (added)
+++ llvm/trunk/test/Transforms/LoopVectorize/if-conversion-nest.ll Fri May 3 12:42:55 2013
@@ -0,0 +1,48 @@
+; RUN: opt < %s -loop-vectorize -force-vector-unroll=1 -force-vector-width=4 -enable-if-conversion -dce -instcombine -S | FileCheck %s
+
+target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
+
+;CHECK: @foo
+;CHECK: icmp sgt
+;CHECK: icmp sgt
+;CHECK: icmp slt
+;CHECK: select <4 x i1>
+;CHECK: %[[P1:.*]] = select <4 x i1>
+;CHECK: xor <4 x i1>
+;CHECK: and <4 x i1>
+;CHECK: select <4 x i1> %{{.*}}, <4 x i32> %{{.*}}, <4 x i32> %[[P1]]
+;CHECK: ret
+define i32 @foo(i32* nocapture %A, i32* nocapture %B, i32 %n) {
+entry:
+ %cmp26 = icmp sgt i32 %n, 0
+ br i1 %cmp26, label %for.body, label %for.end
+
+for.body:
+ %indvars.iv = phi i64 [ %indvars.iv.next, %if.end14 ], [ 0, %entry ]
+ %arrayidx = getelementptr inbounds i32* %A, i64 %indvars.iv
+ %0 = load i32* %arrayidx, align 4
+ %arrayidx2 = getelementptr inbounds i32* %B, i64 %indvars.iv
+ %1 = load i32* %arrayidx2, align 4
+ %cmp3 = icmp sgt i32 %0, %1
+ br i1 %cmp3, label %if.then, label %if.end14
+
+if.then:
+ %cmp6 = icmp sgt i32 %0, 19
+ br i1 %cmp6, label %if.end14, label %if.else
+
+if.else:
+ %cmp10 = icmp slt i32 %1, 4
+ %. = select i1 %cmp10, i32 4, i32 5
+ br label %if.end14
+
+if.end14:
+ %x.0 = phi i32 [ 9, %for.body ], [ 3, %if.then ], [ %., %if.else ] ; <------------- A PHI with 3 entries that we can still vectorize.
+ store i32 %x.0, i32* %arrayidx, align 4
+ %indvars.iv.next = add i64 %indvars.iv, 1
+ %lftr.wideiv = trunc i64 %indvars.iv.next to i32
+ %exitcond = icmp eq i32 %lftr.wideiv, %n
+ br i1 %exitcond, label %for.end, label %for.body
+
+for.end:
+ ret i32 undef
+}
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