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Simplify [su]max(MAX, n) to MAX. This comes up in loop tripcount 

computations in loops with multiple exits.

Adjust the testcase for PR4436 so that the relevant portion isn't
optimized away.

llvm-svn: 74073
This commit is contained in:
Dan Gohman 2009-06-24 14:46:22 +00:00
parent 929fa7b0f4
commit f57bdb75d4
3 changed files with 76 additions and 5 deletions
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12
llvm/lib/Analysis/ScalarEvolution.cpp
View File

@ -1690,10 +1690,14 @@ ScalarEvolution::getSMaxExpr(SmallVectorImpl<const SCEV*> &Ops) {
LHSC = cast<SCEVConstant>(Ops[0]);
}
// If we are left with a constant -inf, strip it off.
// If we are left with a constant minimum-int, strip it off.
if (cast<SCEVConstant>(Ops[0])->getValue()->isMinValue(true)) {
Ops.erase(Ops.begin());
--Idx;
} else if (cast<SCEVConstant>(Ops[0])->getValue()->isMaxValue(true)) {
// If we have an smax with a constant maximum-int, it will always be
// maximum-int.
return Ops[0];
}
}
@ -1777,10 +1781,14 @@ ScalarEvolution::getUMaxExpr(SmallVectorImpl<const SCEV*> &Ops) {
LHSC = cast<SCEVConstant>(Ops[0]);
}
// If we are left with a constant zero, strip it off.
// If we are left with a constant minimum-int, strip it off.
if (cast<SCEVConstant>(Ops[0])->getValue()->isMinValue(false)) {
Ops.erase(Ops.begin());
--Idx;
} else if (cast<SCEVConstant>(Ops[0])->getValue()->isMaxValue(false)) {
// If we have an umax with a constant maximum-int, it will always be
// maximum-int.
return Ops[0];
}
}

6
llvm/test/Transforms/IndVarSimplify/loop_evaluate7.ll
View File

@ -4,7 +4,7 @@
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-f80:32:32"
target triple = "i386-pc-linux-gnu"
define i8* @string_expandtabs() nounwind {
define i8* @string_expandtabs(i32 %n, i8* %m) nounwind {
entry:
br i1 undef, label %bb33, label %bb1
@ -22,11 +22,11 @@ bb19: ; preds = %bb30
bb20: ; preds = %bb19
%0 = load i32* undef, align 4 ; <i32> [#uses=1]
%1 = sub i32 %0, undef ; <i32> [#uses=1]
%1 = sub i32 %0, %n ; <i32> [#uses=1]
br label %bb23
bb21: ; preds = %bb23
%2 = icmp ult i8* %q.0, undef ; <i1> [#uses=1]
%2 = icmp ult i8* %q.0, %m ; <i1> [#uses=1]
br i1 %2, label %bb22, label %overflow2
bb22: ; preds = %bb21

63
llvm/test/Transforms/IndVarSimplify/loop_evaluate8.ll Normal file
View File

@ -0,0 +1,63 @@
; RUN: llvm-as < %s | opt -indvars | llvm-dis | not grep select
; This loop has backedge-taken-count zero. Indvars shouldn't expand any
; instructions to compute a trip count.
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-f80:32:32"
target triple = "i386-pc-linux-gnu"
define i8* @string_expandtabs() nounwind {
entry:
br i1 undef, label %bb33, label %bb1
bb1: ; preds = %entry
br i1 undef, label %overflow1, label %bb15
bb15: ; preds = %bb1
br i1 undef, label %bb33, label %bb17
bb17: ; preds = %bb15
br label %bb30
bb19: ; preds = %bb30
br i1 undef, label %bb20, label %bb29
bb20: ; preds = %bb19
%0 = load i32* undef, align 4 ; <i32> [#uses=1]
%1 = sub i32 %0, undef ; <i32> [#uses=1]
br label %bb23
bb21: ; preds = %bb23
%2 = icmp ult i8* %q.0, undef ; <i1> [#uses=1]
br i1 %2, label %bb22, label %overflow2
bb22: ; preds = %bb21
%3 = getelementptr i8* %q.0, i32 1 ; <i8*> [#uses=1]
br label %bb23
bb23: ; preds = %bb22, %bb20
%i.2 = phi i32 [ %1, %bb20 ], [ %4, %bb22 ] ; <i32> [#uses=1]
%q.0 = phi i8* [ undef, %bb20 ], [ %3, %bb22 ] ; <i8*> [#uses=3]
%4 = add i32 %i.2, -1 ; <i32> [#uses=2]
%5 = icmp eq i32 %4, -1 ; <i1> [#uses=1]
br i1 %5, label %bb29, label %bb21
bb29: ; preds = %bb23, %bb19
%q.1 = phi i8* [ undef, %bb19 ], [ %q.0, %bb23 ] ; <i8*> [#uses=0]
br label %bb30
bb30: ; preds = %bb29, %bb17
br i1 undef, label %bb19, label %bb33
overflow2: ; preds = %bb21
br i1 undef, label %bb32, label %overflow1
bb32: ; preds = %overflow2
br label %overflow1
overflow1: ; preds = %bb32, %overflow2, %bb1
ret i8* null
bb33: ; preds = %bb30, %bb15, %entry
ret i8* undef
}