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improve switch formation to handle small range

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comparisons formed by comparisons.  For example,
this:

void foo(unsigned x) {
  if (x == 0 || x == 1 || x == 3 || x == 4 || x == 6) 
    bar();
}

compiles into:

_foo:                                   ## @foo
## BB#0:                                ## %entry
	cmpl	$6, %edi
	ja	LBB0_2
## BB#1:                                ## %entry
	movl	%edi, %eax
	movl	$91, %ecx
	btq	%rax, %rcx
	jb	LBB0_3

instead of:

_foo:                                   ## @foo
## BB#0:                                ## %entry
	cmpl	$2, %edi
	jb	LBB0_4
## BB#1:                                ## %switch.early.test
	cmpl	$6, %edi
	ja	LBB0_3
## BB#2:                                ## %switch.early.test
	movl	%edi, %eax
	movl	$88, %ecx
	btq	%rax, %rcx
	jb	LBB0_4

This catches a bunch of cases in GCC, which look like this:

 %804 = load i32* @which_alternative, align 4, !tbaa !0
 %805 = icmp ult i32 %804, 2
 %806 = icmp eq i32 %804, 3
 %or.cond121 = or i1 %805, %806
 %807 = icmp eq i32 %804, 4
 %or.cond124 = or i1 %or.cond121, %807
 br i1 %or.cond124, label %.thread, label %808

turning this into a range comparison.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@122045 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2010-12-17 06:20:15 +00:00
parent 1139d5090a
commit e27db74a60
3 changed files with 96 additions and 4 deletions
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2
include/llvm/Support/ConstantRange.h
View File

@ -54,7 +54,7 @@ public:
/// @brief Initialize a range of values explicitly. This will assert out if
/// Lower==Upper and Lower != Min or Max value for its type. It will also
/// assert out if the two APInt's are not the same bit width.
ConstantRange(const APInt& Lower, const APInt& Upper);
ConstantRange(const APInt &Lower, const APInt &Upper);
/// makeICmpRegion - Produce the smallest range that contains all values that
/// might satisfy the comparison specified by Pred when compared to any value

27
lib/Transforms/Utils/SimplifyCFG.cpp
View File

@ -28,6 +28,7 @@
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/Support/CFG.h"
#include "llvm/Support/ConstantRange.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include <algorithm>
@ -305,11 +306,33 @@ GatherConstantCompares(Value *V, std::vector<ConstantInt*> &Vals, Value *&Extra,
// If this is an icmp against a constant, handle this as one of the cases.
if (ICmpInst *ICI = dyn_cast<ICmpInst>(I)) {
if (ICI->getPredicate() == (isEQ ? ICmpInst::ICMP_EQ : ICmpInst::ICMP_NE))
if (ConstantInt *C = GetConstantInt(I->getOperand(1), TD)) {
if (ConstantInt *C = GetConstantInt(I->getOperand(1), TD)) {
if (ICI->getPredicate() == (isEQ ? ICmpInst::ICMP_EQ:ICmpInst::ICMP_NE)) {
Vals.push_back(C);
return I->getOperand(0);
}
// If we have "x ult 3" comparison, for example, then we can add 0,1,2 to
// the set.
ConstantRange Span =
ConstantRange::makeICmpRegion(ICI->getPredicate(),
ConstantRange(C->getValue()));
// If this is an and/!= check then we want to optimize "x ugt 2" into
// x != 0 && x != 1.
if (!isEQ)
Span = Span.inverse();
// If there are a ton of values, we don't want to make a ginormous switch.
if (Span.getSetSize().getZExtValue() > 8 || Span.isEmptySet() ||
// We don't handle wrapped sets yet.
Span.isWrappedSet())
return 0;
for (APInt Tmp = Span.getLower(); Tmp != Span.getUpper(); ++Tmp)
Vals.push_back(ConstantInt::get(V->getContext(), Tmp));
return I->getOperand(0);
}
return 0;
}

71
test/Transforms/SimplifyCFG/switch_create.ll
View File

@ -351,4 +351,73 @@ malformed:
ret void
; CHECK: @test12
}
}
; test13 - handle switch formation with ult.
define void @test13(i32 %x) nounwind ssp noredzone {
entry:
%cmp = icmp ult i32 %x, 2
br i1 %cmp, label %if.then, label %lor.lhs.false3
lor.lhs.false3: ; preds = %lor.lhs.false
%cmp5 = icmp eq i32 %x, 3
br i1 %cmp5, label %if.then, label %lor.lhs.false6
lor.lhs.false6: ; preds = %lor.lhs.false3
%cmp8 = icmp eq i32 %x, 4
br i1 %cmp8, label %if.then, label %lor.lhs.false9
lor.lhs.false9: ; preds = %lor.lhs.false6
%cmp11 = icmp eq i32 %x, 6
br i1 %cmp11, label %if.then, label %if.end
if.then: ; preds = %lor.lhs.false9, %lor.lhs.false6, %lor.lhs.false3, %lor.lhs.false, %entry
call void @foo1() noredzone
br label %if.end
if.end: ; preds = %if.then, %lor.lhs.false9
ret void
; CHECK: @test13
; CHECK: switch i32 %x, label %if.end [
; CHECK: i32 6, label %if.then
; CHECK: i32 4, label %if.then
; CHECK: i32 3, label %if.then
; CHECK: i32 1, label %if.then
; CHECK: i32 0, label %if.then
; CHECK: ]
}
; test14 - handle switch formation with ult.
define void @test14(i32 %x) nounwind ssp noredzone {
entry:
%cmp = icmp ugt i32 %x, 2
br i1 %cmp, label %lor.lhs.false3, label %if.then
lor.lhs.false3: ; preds = %lor.lhs.false
%cmp5 = icmp ne i32 %x, 3
br i1 %cmp5, label %lor.lhs.false6, label %if.then
lor.lhs.false6: ; preds = %lor.lhs.false3
%cmp8 = icmp ne i32 %x, 4
br i1 %cmp8, label %lor.lhs.false9, label %if.then
lor.lhs.false9: ; preds = %lor.lhs.false6
%cmp11 = icmp ne i32 %x, 6
br i1 %cmp11, label %if.end, label %if.then
if.then: ; preds = %lor.lhs.false9, %lor.lhs.false6, %lor.lhs.false3, %lor.lhs.false, %entry
call void @foo1() noredzone
br label %if.end
if.end: ; preds = %if.then, %lor.lhs.false9
ret void
; CHECK: @test14
; CHECK: switch i32 %x, label %if.end [
; CHECK: i32 6, label %if.then
; CHECK: i32 4, label %if.then
; CHECK: i32 3, label %if.then
; CHECK: i32 1, label %if.then
; CHECK: i32 0, label %if.then
; CHECK: ]
}