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[TTI] Teach the cost heuristic how to query TLI to check if a zext/trunc is 'free' for the target.

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Now that SimplifyCFG uses TTI for the cost heuristic, we can teach BasicTTIImpl
how to query TLI in order to get a more accurate cost for truncates and
zero-extends.

Before this patch, the basic cost heuristic in TargetTransformInfoImplCRTPBase
would have conservatively returned a 'default' TCC_Basic for all zero-extends,
and TCC_Free for truncates on native types.

This patch improves the heuristic so that we query TLI (if available) to get
more accurate answers. If TLI is available, then methods 'isZExtFree' and
'isTruncateFree' can be used to check if a zext/trunc is free for the target.

Added more test cases to SimplifyCFG/X86/speculate-cttz-ctlz.ll.
With this change, SimplifyCFG is now able to speculate a 'cheap' cttz/ctlz
immediately followed by a free zext/trunc.

Differential Revision: http://reviews.llvm.org/D7585


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@228923 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Andrea Di Biagio 2015-02-12 14:17:24 +00:00
parent c70b2070db
commit 44926033f6
3 changed files with 209 additions and 2 deletions
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3
include/llvm/Analysis/TargetTransformInfoImpl.h
View File

@ -421,8 +421,7 @@ public:
return TTI::TCC_Free;
}
// Otherwise delegate to the fully generic implementations.
return getOperationCost(
return static_cast<T *>(this)->getOperationCost(
Operator::getOpcode(U), U->getType(),
U->getNumOperands() == 1 ? U->getOperand(0)->getType() : nullptr);
}

19
include/llvm/CodeGen/BasicTTIImpl.h
View File

@ -195,6 +195,25 @@ public:
return TargetTransformInfo::TCC_Basic;
}
unsigned getOperationCost(unsigned Opcode, Type *Ty, Type *OpTy) {
const TargetLoweringBase *TLI = getTLI();
switch (Opcode) {
default: break;
case Instruction::Trunc: {
if (TLI->isTruncateFree(OpTy, Ty))
return TargetTransformInfo::TCC_Free;
return TargetTransformInfo::TCC_Basic;
}
case Instruction::ZExt: {
if (TLI->isZExtFree(OpTy, Ty))
return TargetTransformInfo::TCC_Free;
return TargetTransformInfo::TCC_Basic;
}
}
return BaseT::getOperationCost(Opcode, Ty, OpTy);
}
void getUnrollingPreferences(Loop *L, TTI::UnrollingPreferences &UP) {
// This unrolling functionality is target independent, but to provide some
// motivation for its intended use, for x86:

189
test/Transforms/SimplifyCFG/X86/speculate-cttz-ctlz.ll
View File

@ -133,6 +133,195 @@ cond.end: ; preds = %entry, %cond.true
ret i16 %cond
}
; The following tests verify that calls to cttz/ctlz are speculated even if
; basic block %cond.true has an extra zero extend/truncate which is "free"
; for the target.
define i64 @test1e(i32 %x) {
; ALL-LABEL: @test1e(
; ALL: [[COND:%[A-Za-z0-9]+]] = icmp eq i32 %x, 0
; ALL: [[CTTZ:%[A-Za-z0-9]+]] = tail call i32 @llvm.cttz.i32(i32 %x, i1 true)
; ALL: [[ZEXT:%[A-Za-z0-9]+]] = zext i32 [[CTTZ]] to i64
; BMI-NEXT: select i1 [[COND]], i64 32, i64 [[ZEXT]]
; LZCNT-NOT: select
; GENERIC-NOT: select
; ALL: ret
entry:
%tobool = icmp eq i32 %x, 0
br i1 %tobool, label %cond.end, label %cond.true
cond.true: ; preds = %entry
%0 = tail call i32 @llvm.cttz.i32(i32 %x, i1 true)
%phitmp2 = zext i32 %0 to i64
br label %cond.end
cond.end: ; preds = %entry, %cond.true
%cond = phi i64 [ %phitmp2, %cond.true ], [ 32, %entry ]
ret i64 %cond
}
define i32 @test2e(i64 %x) {
; ALL-LABEL: @test2e(
; ALL: [[COND:%[A-Za-z0-9]+]] = icmp eq i64 %x, 0
; ALL: [[CTTZ:%[A-Za-z0-9]+]] = tail call i64 @llvm.cttz.i64(i64 %x, i1 true)
; ALL: [[TRUNC:%[A-Za-z0-9]+]] = trunc i64 [[CTTZ]] to i32
; BMI-NEXT: select i1 [[COND]], i32 64, i32 [[TRUNC]]
; LZCNT-NOT: select
; GENERIC-NOT: select
; ALL: ret
entry:
%tobool = icmp eq i64 %x, 0
br i1 %tobool, label %cond.end, label %cond.true
cond.true: ; preds = %entry
%0 = tail call i64 @llvm.cttz.i64(i64 %x, i1 true)
%cast = trunc i64 %0 to i32
br label %cond.end
cond.end: ; preds = %entry, %cond.true
%cond = phi i32 [ %cast, %cond.true ], [ 64, %entry ]
ret i32 %cond
}
define i64 @test3e(i32 %x) {
; ALL-LABEL: @test3e(
; ALL: [[COND:%[A-Za-z0-9]+]] = icmp eq i32 %x, 0
; ALL: [[CTLZ:%[A-Za-z0-9]+]] = tail call i32 @llvm.ctlz.i32(i32 %x, i1 true)
; ALL: [[ZEXT:%[A-Za-z0-9]+]] = zext i32 [[CTLZ]] to i64
; LZCNT-NEXT: select i1 [[COND]], i64 32, i64 [[ZEXT]]
; BMI-NOT: select
; GENERIC-NOT: select
; ALL: ret
entry:
%tobool = icmp eq i32 %x, 0
br i1 %tobool, label %cond.end, label %cond.true
cond.true: ; preds = %entry
%0 = tail call i32 @llvm.ctlz.i32(i32 %x, i1 true)
%phitmp2 = zext i32 %0 to i64
br label %cond.end
cond.end: ; preds = %entry, %cond.true
%cond = phi i64 [ %phitmp2, %cond.true ], [ 32, %entry ]
ret i64 %cond
}
define i32 @test4e(i64 %x) {
; ALL-LABEL: @test4e(
; ALL: [[COND:%[A-Za-z0-9]+]] = icmp eq i64 %x, 0
; ALL: [[CTLZ:%[A-Za-z0-9]+]] = tail call i64 @llvm.ctlz.i64(i64 %x, i1 true)
; ALL: [[TRUNC:%[A-Za-z0-9]+]] = trunc i64 [[CTLZ]] to i32
; LZCNT-NEXT: select i1 [[COND]], i32 64, i32 [[TRUNC]]
; BMI-NOT: select
; GENERIC-NOT: select
; ALL: ret
entry:
%tobool = icmp eq i64 %x, 0
br i1 %tobool, label %cond.end, label %cond.true
cond.true: ; preds = %entry
%0 = tail call i64 @llvm.ctlz.i64(i64 %x, i1 true)
%cast = trunc i64 %0 to i32
br label %cond.end
cond.end: ; preds = %entry, %cond.true
%cond = phi i32 [ %cast, %cond.true ], [ 64, %entry ]
ret i32 %cond
}
define i16 @test5e(i64 %x) {
; ALL-LABEL: @test5e(
; ALL: [[COND:%[A-Za-z0-9]+]] = icmp eq i64 %x, 0
; ALL: [[CTLZ:%[A-Za-z0-9]+]] = tail call i64 @llvm.ctlz.i64(i64 %x, i1 true)
; ALL: [[TRUNC:%[A-Za-z0-9]+]] = trunc i64 [[CTLZ]] to i16
; LZCNT-NEXT: select i1 [[COND]], i16 64, i16 [[TRUNC]]
; BMI-NOT: select
; GENERIC-NOT: select
; ALL: ret
entry:
%tobool = icmp eq i64 %x, 0
br i1 %tobool, label %cond.end, label %cond.true
cond.true: ; preds = %entry
%0 = tail call i64 @llvm.ctlz.i64(i64 %x, i1 true)
%cast = trunc i64 %0 to i16
br label %cond.end
cond.end: ; preds = %entry, %cond.true
%cond = phi i16 [ %cast, %cond.true ], [ 64, %entry ]
ret i16 %cond
}
define i16 @test6e(i32 %x) {
; ALL-LABEL: @test6e(
; ALL: [[COND:%[A-Za-z0-9]+]] = icmp eq i32 %x, 0
; ALL: [[CTLZ:%[A-Za-z0-9]+]] = tail call i32 @llvm.ctlz.i32(i32 %x, i1 true)
; ALL: [[TRUNC:%[A-Za-z0-9]+]] = trunc i32 [[CTLZ]] to i16
; LZCNT-NEXT: select i1 [[COND]], i16 32, i16 [[TRUNC]]
; BMI-NOT: select
; GENERIC-NOT: select
; ALL: ret
entry:
%tobool = icmp eq i32 %x, 0
br i1 %tobool, label %cond.end, label %cond.true
cond.true: ; preds = %entry
%0 = tail call i32 @llvm.ctlz.i32(i32 %x, i1 true)
%cast = trunc i32 %0 to i16
br label %cond.end
cond.end: ; preds = %entry, %cond.true
%cond = phi i16 [ %cast, %cond.true ], [ 32, %entry ]
ret i16 %cond
}
define i16 @test7e(i64 %x) {
; ALL-LABEL: @test7e(
; ALL: [[COND:%[A-Za-z0-9]+]] = icmp eq i64 %x, 0
; ALL: [[CTTZ:%[A-Za-z0-9]+]] = tail call i64 @llvm.cttz.i64(i64 %x, i1 true)
; ALL: [[TRUNC:%[A-Za-z0-9]+]] = trunc i64 [[CTTZ]] to i16
; BMI-NEXT: select i1 [[COND]], i16 64, i16 [[TRUNC]]
; LZCNT-NOT: select
; GENERIC-NOT: select
; ALL: ret
entry:
%tobool = icmp eq i64 %x, 0
br i1 %tobool, label %cond.end, label %cond.true
cond.true: ; preds = %entry
%0 = tail call i64 @llvm.cttz.i64(i64 %x, i1 true)
%cast = trunc i64 %0 to i16
br label %cond.end
cond.end: ; preds = %entry, %cond.true
%cond = phi i16 [ %cast, %cond.true ], [ 64, %entry ]
ret i16 %cond
}
define i16 @test8e(i32 %x) {
; ALL-LABEL: @test8e(
; ALL: [[COND:%[A-Za-z0-9]+]] = icmp eq i32 %x, 0
; ALL: [[CTTZ:%[A-Za-z0-9]+]] = tail call i32 @llvm.cttz.i32(i32 %x, i1 true)
; ALL: [[TRUNC:%[A-Za-z0-9]+]] = trunc i32 [[CTTZ]] to i16
; BMI-NEXT: select i1 [[COND]], i16 32, i16 [[TRUNC]]
; LZCNT-NOT: select
; GENERIC-NOT: select
; ALL: ret
entry:
%tobool = icmp eq i32 %x, 0
br i1 %tobool, label %cond.end, label %cond.true
cond.true: ; preds = %entry
%0 = tail call i32 @llvm.cttz.i32(i32 %x, i1 true)
%cast = trunc i32 %0 to i16
br label %cond.end
cond.end: ; preds = %entry, %cond.true
%cond = phi i16 [ %cast, %cond.true ], [ 32, %entry ]
ret i16 %cond
}
declare i64 @llvm.ctlz.i64(i64, i1)
declare i32 @llvm.ctlz.i32(i32, i1)
declare i16 @llvm.ctlz.i16(i16, i1)