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https://github.com/RPCS3/llvm-mirror.git
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improve switch formation to handle small range
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.
llvm-svn: 122045
This commit is contained in:
Chris Lattner
parent
eea7fd1c3e
commit
e92f8121d4
@ -54,7 +54,7 @@ public:
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/// @brief Initialize a range of values explicitly. This will assert out if
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/// Lower==Upper and Lower != Min or Max value for its type. It will also
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/// assert out if the two APInt's are not the same bit width.
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ConstantRange(const APInt& Lower, const APInt& Upper);
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ConstantRange(const APInt &Lower, const APInt &Upper);
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/// makeICmpRegion - Produce the smallest range that contains all values that
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/// might satisfy the comparison specified by Pred when compared to any value
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@ -28,6 +28,7 @@
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#include "llvm/ADT/Statistic.h"
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#include "llvm/ADT/STLExtras.h"
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#include "llvm/Support/CFG.h"
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#include "llvm/Support/ConstantRange.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/raw_ostream.h"
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#include <algorithm>
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@ -305,11 +306,33 @@ GatherConstantCompares(Value *V, std::vector<ConstantInt*> &Vals, Value *&Extra,
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// If this is an icmp against a constant, handle this as one of the cases.
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if (ICmpInst *ICI = dyn_cast<ICmpInst>(I)) {
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if (ICI->getPredicate() == (isEQ ? ICmpInst::ICMP_EQ : ICmpInst::ICMP_NE))
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if (ConstantInt *C = GetConstantInt(I->getOperand(1), TD)) {
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if (ConstantInt *C = GetConstantInt(I->getOperand(1), TD)) {
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if (ICI->getPredicate() == (isEQ ? ICmpInst::ICMP_EQ:ICmpInst::ICMP_NE)) {
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Vals.push_back(C);
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return I->getOperand(0);
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}
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// If we have "x ult 3" comparison, for example, then we can add 0,1,2 to
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// the set.
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ConstantRange Span =
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ConstantRange::makeICmpRegion(ICI->getPredicate(),
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ConstantRange(C->getValue()));
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// If this is an and/!= check then we want to optimize "x ugt 2" into
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// x != 0 && x != 1.
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if (!isEQ)
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Span = Span.inverse();
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// If there are a ton of values, we don't want to make a ginormous switch.
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if (Span.getSetSize().getZExtValue() > 8 || Span.isEmptySet() ||
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// We don't handle wrapped sets yet.
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Span.isWrappedSet())
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return 0;
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for (APInt Tmp = Span.getLower(); Tmp != Span.getUpper(); ++Tmp)
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Vals.push_back(ConstantInt::get(V->getContext(), Tmp));
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return I->getOperand(0);
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}
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return 0;
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}
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@ -351,4 +351,73 @@ malformed:
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ret void
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; CHECK: @test12
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}
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}
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; test13 - handle switch formation with ult.
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define void @test13(i32 %x) nounwind ssp noredzone {
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entry:
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%cmp = icmp ult i32 %x, 2
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br i1 %cmp, label %if.then, label %lor.lhs.false3
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lor.lhs.false3: ; preds = %lor.lhs.false
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%cmp5 = icmp eq i32 %x, 3
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br i1 %cmp5, label %if.then, label %lor.lhs.false6
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lor.lhs.false6: ; preds = %lor.lhs.false3
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%cmp8 = icmp eq i32 %x, 4
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br i1 %cmp8, label %if.then, label %lor.lhs.false9
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lor.lhs.false9: ; preds = %lor.lhs.false6
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%cmp11 = icmp eq i32 %x, 6
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br i1 %cmp11, label %if.then, label %if.end
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if.then: ; preds = %lor.lhs.false9, %lor.lhs.false6, %lor.lhs.false3, %lor.lhs.false, %entry
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call void @foo1() noredzone
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br label %if.end
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if.end: ; preds = %if.then, %lor.lhs.false9
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ret void
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; CHECK: @test13
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; CHECK: switch i32 %x, label %if.end [
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; CHECK: i32 6, label %if.then
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; CHECK: i32 4, label %if.then
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; CHECK: i32 3, label %if.then
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; CHECK: i32 1, label %if.then
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; CHECK: i32 0, label %if.then
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; CHECK: ]
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}
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; test14 - handle switch formation with ult.
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define void @test14(i32 %x) nounwind ssp noredzone {
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entry:
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%cmp = icmp ugt i32 %x, 2
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br i1 %cmp, label %lor.lhs.false3, label %if.then
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lor.lhs.false3: ; preds = %lor.lhs.false
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%cmp5 = icmp ne i32 %x, 3
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br i1 %cmp5, label %lor.lhs.false6, label %if.then
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lor.lhs.false6: ; preds = %lor.lhs.false3
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%cmp8 = icmp ne i32 %x, 4
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br i1 %cmp8, label %lor.lhs.false9, label %if.then
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lor.lhs.false9: ; preds = %lor.lhs.false6
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%cmp11 = icmp ne i32 %x, 6
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br i1 %cmp11, label %if.end, label %if.then
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if.then: ; preds = %lor.lhs.false9, %lor.lhs.false6, %lor.lhs.false3, %lor.lhs.false, %entry
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call void @foo1() noredzone
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br label %if.end
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if.end: ; preds = %if.then, %lor.lhs.false9
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ret void
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; CHECK: @test14
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; CHECK: switch i32 %x, label %if.end [
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; CHECK: i32 6, label %if.then
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; CHECK: i32 4, label %if.then
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; CHECK: i32 3, label %if.then
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; CHECK: i32 1, label %if.then
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; CHECK: i32 0, label %if.then
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; CHECK: ]
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}
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