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[SimplifyIndVars] Ignore dead users 

IndVarSimplify sometimes makes transforms basing on users that are trivially dead. In particular,
if DCE wasn't run before it, there may be a dead `sext/zext` in loop that will trigger widening
transforms, however it makes no sense to do it.

This patch teaches IndVarsSimplify ignore the mist trivial cases of that.

Differential Revision: https://reviews.llvm.org/D47974
Reviewed By: sanjoy

llvm-svn: 334567
This commit is contained in:
Max Kazantsev 2018-06-13 02:25:32 +00:00
parent 8472ec9663
commit 0ed79620c6
9 changed files with 72 additions and 2 deletions
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10
llvm/lib/Transforms/Utils/SimplifyIndVar.cpp
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@ -26,6 +26,7 @@
#include "llvm/IR/PatternMatch.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/Utils/Local.h"
using namespace llvm;
@ -772,6 +773,15 @@ void SimplifyIndvar::simplifyUsers(PHINode *CurrIV, IVVisitor *V) {
SimpleIVUsers.pop_back_val();
Instruction *UseInst = UseOper.first;
// If a user of the IndVar is trivially dead, we prefer just to mark it dead
// rather than try to do some complex analysis or transformation (such as
// widening) basing on it.
// TODO: Propagate TLI and pass it here to handle more cases.
if (isInstructionTriviallyDead(UseInst, /* TLI */ nullptr)) {
DeadInsts.emplace_back(UseInst);
continue;
}
// Bypass back edges to avoid extra work.
if (UseInst == CurrIV) continue;

4
llvm/test/Analysis/ScalarEvolution/2012-05-29-MulAddRec.ll
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@ -8,6 +8,8 @@
;
; PR12929: cast<Ty>() argument of incompatible type
declare void @use(i8 %x)
; CHECK: @func
; CHECK: for.cond:
; CHECK: %inc1 = phi i8 [ 0, %entry ], [ %0, %for.body ]
@ -33,6 +35,7 @@ for.cond: ; preds = %for.cond.loopexit,
%indvars.iv = phi i8 [ %indvars.iv.next, %for.cond.loopexit ], [ 10, %entry ]
%mul3 = phi i8 [ undef, %entry ], [ %mul.lcssa, %for.cond.loopexit ]
%inc1 = phi i8 [ 0, %entry ], [ %0, %for.cond.loopexit ]
call void @use(i8 %inc1)
br label %for.body
for.body: ; preds = %for.body, %for.cond
@ -40,6 +43,7 @@ for.body: ; preds = %for.body, %for.cond
%mul45 = phi i8 [ %mul3, %for.cond ], [ %mul, %for.body ]
%inc = add i8 %inc26, 1
%mul = mul i8 %inc26, %mul45
call void @use(i8 %inc)
%exitcond = icmp ne i8 %inc, %indvars.iv
br i1 %exitcond, label %for.body, label %for.cond.loopexit
}

3
llvm/test/Analysis/ScalarEvolution/guards.ll
View File

@ -10,6 +10,8 @@ target datalayout = "n8:16:32:64"
declare void @llvm.experimental.guard(i1, ...)
declare void @use(i64 %x)
define void @test_1(i1* %cond_buf, i32* %len_buf) {
; CHECK-LABEL: @test_1(
entry:
@ -60,6 +62,7 @@ loop:
%iv.inc = add i32 %iv, 1
%iv.sext = sext i32 %iv to i64
call void @use(i64 %iv.sext)
%iv.inc.cmp = icmp slt i32 %iv.inc, %len
call void(i1, ...) @llvm.experimental.guard(i1 %iv.inc.cmp) [ "deopt"() ]

6
llvm/test/Transforms/IndVarSimplify/2011-09-10-widen-nsw.ll
View File

@ -5,6 +5,8 @@
target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64"
declare void @use(i64 %x)
define void @test() nounwind {
entry:
br i1 undef, label %for.body11, label %for.end285
@ -26,15 +28,19 @@ for.body170: ; preds = %for.body170, %for.b
%add = add nsw i32 %i2.19, 1
%add.idxprom = sext i32 %add to i64
call void @use(i64 %add.idxprom)
%sub = sub nsw i32 %i2.19, 2
%sub.idxprom = sext i32 %sub to i64
call void @use(i64 %sub.idxprom)
%sub.neg = sub nsw i32 4, %i2.19
%sub.neg.idxprom = sext i32 %sub.neg to i64
call void @use(i64 %sub.neg.idxprom)
%mul = mul nsw i32 %i2.19, 8
%mul.idxprom = sext i32 %mul to i64
call void @use(i64 %mul.idxprom)
%add249 = add nsw i32 %i2.19, %shl132
br label %for.body170

35
llvm/test/Transforms/IndVarSimplify/iv-widen.ll
View File

@ -7,10 +7,12 @@ target datalayout = "n8:16:32:64"
target triple = "x86_64-apple-darwin"
declare void @use(i64 %x)
; CHECK-LABEL: @loop_0
; CHECK-LABEL: B18:
; Only one phi now.
; CHECK: phi
; CHECK: phi i64
; CHECK-NOT: phi
; One trunc for the gep.
; CHECK: trunc i64 %indvars.iv to i32
@ -21,6 +23,37 @@ define void @loop_0(i32* %a) {
Prologue:
br i1 undef, label %B18, label %B6
B18: ; preds = %B24, %Prologue
%.02 = phi i32 [ 0, %Prologue ], [ %tmp33, %B24 ]
%tmp23 = zext i32 %.02 to i64
call void @use(i64 %tmp23)
%tmp33 = add i32 %.02, 1
%o = getelementptr i32, i32* %a, i32 %.02
%v = load i32, i32* %o
%t = icmp eq i32 %v, 0
br i1 %t, label %exit24, label %B24
B24: ; preds = %B18
%t2 = icmp eq i32 %tmp33, 20
br i1 %t2, label %B6, label %B18
B6: ; preds = %Prologue
ret void
exit24: ; preds = %B18
call void @dummy(i32 %.02)
unreachable
}
; Make sure that dead zext is removed and no widening happens.
; CHECK-LABEL: @loop_0.dead
; CHECK: phi i32
; CHECK-NOT: zext
; CHECK-NOT: trunc
define void @loop_0.dead(i32* %a) {
Prologue:
br i1 undef, label %B18, label %B6
B18: ; preds = %B24, %Prologue
%.02 = phi i32 [ 0, %Prologue ], [ %tmp33, %B24 ]
%tmp23 = zext i32 %.02 to i64

5
llvm/test/Transforms/IndVarSimplify/lftr-reuse.ll
View File

@ -6,6 +6,8 @@ target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f3
; Perform LFTR using the original pointer-type IV.
declare void @use(double %x)
; for(char* p = base; p < base + n; ++p) {
; *p = p-base;
; }
@ -102,9 +104,11 @@ loop:
%diagidxw = sext i32 %diagidx to i64
%matrixp = getelementptr inbounds [0 x double], [0 x double]* %matrix, i32 0, i64 %diagidxw
%v1 = load double, double* %matrixp
call void @use(double %v1)
%iw = sext i32 %i to i64
%vectorp = getelementptr inbounds [0 x double], [0 x double]* %vector, i32 0, i64 %iw
%v2 = load double, double* %vectorp
call void @use(double %v2)
%row.inc = add nsw i32 %rowidx, %ilead
%i.inc = add nsw i32 %i, 1
%cmp196 = icmp slt i32 %i.inc, %irow
@ -125,7 +129,6 @@ entry:
; CHECK-NOT: add
; CHECK: loop:
; CHECK: phi i64
; CHECK: phi i64
; CHECK-NOT: phi
; CHECK: icmp slt
; CHECK: br i1

3
llvm/test/Transforms/IndVarSimplify/loop-invariant-conditions.ll
View File

@ -293,6 +293,8 @@ for.end: ; preds = %if.end, %entry
ret void
}
declare void @use(i1 %x)
; check that we handle conditions with loop invariant operands which
; *aren't* in the header - this is a very rare and fragile case where
; we have a "loop" which is known to run exactly one iteration but
@ -320,6 +322,7 @@ latch:
br i1 true, label %exit, label %loop
exit:
call void @use(i1 %cmp)
ret void
}

5
llvm/test/Transforms/IndVarSimplify/no-iv-rewrite.ll
View File

@ -357,6 +357,9 @@ exit:
ret void
}
declare void @use32(i32 %x)
declare void @use64(i64 %x)
; Test a widened IV that is used by a phi on different paths within the loop.
;
; CHECK: for.body:
@ -385,10 +388,12 @@ if.else:
if.then97:
%idxprom100 = sext i32 %iv to i64
call void @use64(i64 %idxprom100)
br label %for.inc
for.inc:
%kmin.1 = phi i32 [ %iv, %if.then33 ], [ 0, %if.then ], [ %iv, %if.then97 ], [ 0, %if.else ]
call void @use32(i32 %kmin.1)
%inc = add nsw i32 %iv, 1
br i1 undef, label %for.body, label %for.end

3
llvm/test/Transforms/IndVarSimplify/pr25578.ll
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@ -1,6 +1,8 @@
; RUN: opt < %s -indvars -S | FileCheck %s
target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
declare void @use(i64 %x)
; CHECK-LABEL: @foo
define void @foo() {
entry:
@ -15,6 +17,7 @@ L1_header:
L2_header:
%i = phi i32 [ 0, %L1_header ], [ %i_next, %L2_latch ]
%i_prom = sext i32 %i to i64
call void @use(i64 %i_prom)
br label %L3_header
L3_header: