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Teach ScalarEvolution to simplify smax and umax when it can prove

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that one operand is always greater than another.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@101142 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dan Gohman 2010-04-13 16:51:03 +00:00
parent 3ab131243e
commit 28287794d4
2 changed files with 66 additions and 2 deletions
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16
lib/Analysis/ScalarEvolution.cpp
View File

@ -2117,7 +2117,13 @@ ScalarEvolution::getSMaxExpr(SmallVectorImpl<const SCEV *> &Ops) {
// so, delete one. Since we sorted the list, these values are required to
// be adjacent.
for (unsigned i = 0, e = Ops.size()-1; i != e; ++i)
if (Ops[i] == Ops[i+1]) { // X smax Y smax Y --> X smax Y
// X smax Y smax Y --> X smax Y
// X smax Y --> X, if X is always greater than Y
if (Ops[i] == Ops[i+1] ||
isKnownPredicate(ICmpInst::ICMP_SGE, Ops[i], Ops[i+1])) {
Ops.erase(Ops.begin()+i+1, Ops.begin()+i+2);
--i; --e;
} else if (isKnownPredicate(ICmpInst::ICMP_SLE, Ops[i], Ops[i+1])) {
Ops.erase(Ops.begin()+i, Ops.begin()+i+1);
--i; --e;
}
@ -2216,7 +2222,13 @@ ScalarEvolution::getUMaxExpr(SmallVectorImpl<const SCEV *> &Ops) {
// so, delete one. Since we sorted the list, these values are required to
// be adjacent.
for (unsigned i = 0, e = Ops.size()-1; i != e; ++i)
if (Ops[i] == Ops[i+1]) { // X umax Y umax Y --> X umax Y
// X umax Y umax Y --> X umax Y
// X umax Y --> X, if X is always greater than Y
if (Ops[i] == Ops[i+1] ||
isKnownPredicate(ICmpInst::ICMP_UGE, Ops[i], Ops[i+1])) {
Ops.erase(Ops.begin()+i+1, Ops.begin()+i+2);
--i; --e;
} else if (isKnownPredicate(ICmpInst::ICMP_ULE, Ops[i], Ops[i+1])) {
Ops.erase(Ops.begin()+i, Ops.begin()+i+1);
--i; --e;
}

52
test/Transforms/IndVarSimplify/eliminate-max.ll Normal file
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@ -0,0 +1,52 @@
; RUN: opt < %s -S -indvars | grep {= icmp} | count 3
; PR4914.ll
; Indvars should be able to do range analysis and eliminate icmps.
; There are two here which cannot be eliminated.
; There's one that icmp which can be eliminated and which indvars currently
; cannot eliminate, because it requires analyzing more than just the
; range of the induction variable.
@0 = private constant [4 x i8] c"%d\0A\00", align 1 ; <[4 x i8]*> [#uses=1]
define i32 @main() nounwind {
bb:
br label %bb1
bb1: ; preds = %bb14, %bb
%t = phi i32 [ 0, %bb ], [ %t19, %bb14 ] ; <i32> [#uses=5]
%t2 = phi i32 [ 0, %bb ], [ %t18, %bb14 ] ; <i32> [#uses=1]
%t3 = icmp slt i32 %t, 0 ; <i1> [#uses=1]
br i1 %t3, label %bb7, label %bb4
bb4: ; preds = %bb1
%t5 = icmp sgt i32 %t, 255 ; <i1> [#uses=1]
%t6 = select i1 %t5, i32 255, i32 %t ; <i32> [#uses=1]
br label %bb7
bb7: ; preds = %bb4, %bb1
%t8 = phi i32 [ %t6, %bb4 ], [ 0, %bb1 ] ; <i32> [#uses=1]
%t9 = sub i32 0, %t ; <i32> [#uses=3]
%t10 = icmp slt i32 %t9, 0 ; <i1> [#uses=1]
br i1 %t10, label %bb14, label %bb11
bb11: ; preds = %bb7
%t12 = icmp sgt i32 %t9, 255 ; <i1> [#uses=1]
%t13 = select i1 %t12, i32 255, i32 %t9 ; <i32> [#uses=1]
br label %bb14
bb14: ; preds = %bb11, %bb7
%t15 = phi i32 [ %t13, %bb11 ], [ 0, %bb7 ] ; <i32> [#uses=1]
%t16 = add nsw i32 %t2, 255 ; <i32> [#uses=1]
%t17 = add nsw i32 %t16, %t8 ; <i32> [#uses=1]
%t18 = add nsw i32 %t17, %t15 ; <i32> [#uses=2]
%t19 = add nsw i32 %t, 1 ; <i32> [#uses=2]
%t20 = icmp slt i32 %t19, 1000000000 ; <i1> [#uses=1]
br i1 %t20, label %bb1, label %bb21
bb21: ; preds = %bb14
%t22 = call i32 (i8*, ...)* @printf(i8* noalias getelementptr inbounds ([4 x i8]* @0, i32 0, i32 0), i32 %t18) nounwind
ret i32 0
}
declare i32 @printf(i8* noalias nocapture, ...) nounwind