[llvm] r232902 - [SimplifyLibCalls] Turn memchr(const, C, const) into a bitfield check.
Benjamin Kramer
benny.kra at googlemail.com
Sat Mar 21 14:09:33 PDT 2015
Author: d0k
Date: Sat Mar 21 16:09:33 2015
New Revision: 232902
URL: http://llvm.org/viewvc/llvm-project?rev=232902&view=rev
Log:
[SimplifyLibCalls] Turn memchr(const, C, const) into a bitfield check.
strchr("123!", C) != nullptr is a common pattern to check if C is one
of 1, 2, 3 or !. If the largest element of the string is smaller than
the target's register size we can easily create a bitfield and just
do a simple test for set membership.
int foo(char C) { return strchr("123!", C) != nullptr; } now becomes
cmpl $64, %edi ## range check
sbbb %al, %al
movabsq $0xE000200000001, %rcx
btq %rdi, %rcx ## bit test
sbbb %cl, %cl
andb %al, %cl ## and the two conditions
andb $1, %cl
movzbl %cl, %eax ## returning an int
ret
(imho the backend should expand this into a series of branches, but
that's a different story)
The code is currently limited to bit fields that fit in a register, so
usually 64 or 32 bits. Sadly, this misses anything using alpha chars
or {}. This could be fixed by just emitting a i128 bit field, but that
can generate really ugly code so we have to find a better way. To some
degree this is also recreating switch lowering logic, but we can't
simply emit a switch instruction and thus change the CFG within
instcombine.
Modified:
llvm/trunk/lib/Target/README.txt
llvm/trunk/lib/Transforms/Utils/SimplifyLibCalls.cpp
llvm/trunk/test/Transforms/InstCombine/memchr.ll
llvm/trunk/test/Transforms/InstCombine/strchr-1.ll
Modified: llvm/trunk/lib/Target/README.txt
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/README.txt?rev=232902&r1=232901&r2=232902&view=diff
==============================================================================
--- llvm/trunk/lib/Target/README.txt (original)
+++ llvm/trunk/lib/Target/README.txt Sat Mar 21 16:09:33 2015
@@ -1268,7 +1268,8 @@ int foo (void) {
..
else if (strchr ("<>", *intel_parser.op_string)
-Those should be turned into a switch.
+Those should be turned into a switch. SimplifyLibCalls only gets the second
+case.
//===---------------------------------------------------------------------===//
Modified: llvm/trunk/lib/Transforms/Utils/SimplifyLibCalls.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/SimplifyLibCalls.cpp?rev=232902&r1=232901&r2=232902&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Utils/SimplifyLibCalls.cpp (original)
+++ llvm/trunk/lib/Transforms/Utils/SimplifyLibCalls.cpp Sat Mar 21 16:09:33 2015
@@ -762,11 +762,9 @@ Value *LibCallSimplifier::optimizeMemChr
if (LenC && LenC->isNullValue())
return Constant::getNullValue(CI->getType());
- // Check if all arguments are constants. If so, we can constant fold.
+ // From now on we need at least constant length and string.
StringRef Str;
- if (!CharC || !LenC ||
- !getConstantStringInfo(SrcStr, Str, /*Offset=*/0,
- /*TrimAtNul=*/false))
+ if (!LenC || !getConstantStringInfo(SrcStr, Str, 0, /*TrimAtNul=*/false))
return nullptr;
// Truncate the string to LenC. If Str is smaller than LenC we will still only
@@ -774,6 +772,54 @@ Value *LibCallSimplifier::optimizeMemChr
// return null if we don't find the char.
Str = Str.substr(0, LenC->getZExtValue());
+ // If the char is variable but the input str and length are not we can turn
+ // this memchr call into a simple bit field test. Of course this only works
+ // when the return value is only checked against null.
+ //
+ // It would be really nice to reuse switch lowering here but we can't change
+ // the CFG at this point.
+ //
+ // memchr("\r\n", C, 2) != nullptr -> (C & ((1 << '\r') | (1 << '\n'))) != 0
+ // after bounds check.
+ if (!CharC && !Str.empty() && isOnlyUsedInZeroEqualityComparison(CI)) {
+ unsigned char Max = *std::max_element(Str.begin(), Str.end());
+
+ // Make sure the bit field we're about to create fits in a register on the
+ // target.
+ // FIXME: On a 64 bit architecture this prevents us from using the
+ // interesting range of alpha ascii chars. We could do better by emitting
+ // two bitfields or shifting the range by 64 if no lower chars are used.
+ if (!DL.fitsInLegalInteger(Max + 1))
+ return nullptr;
+
+ // For the bit field use a power-of-2 type with at least 8 bits to avoid
+ // creating unnecessary illegal types.
+ unsigned char Width = NextPowerOf2(std::max((unsigned char)7, Max));
+
+ // Now build the bit field.
+ APInt Bitfield(Width, 0);
+ for (char C : Str)
+ Bitfield.setBit((unsigned char)C);
+ Value *BitfieldC = B.getInt(Bitfield);
+
+ // First check that the bit field access is within bounds.
+ Value *C = B.CreateZExtOrTrunc(CI->getArgOperand(1), BitfieldC->getType());
+ Value *Bounds = B.CreateICmp(ICmpInst::ICMP_ULT, C, B.getIntN(Width, Width),
+ "memchr.bounds");
+
+ // Create code that checks if the given bit is set in the field.
+ Value *Shl = B.CreateShl(B.getIntN(Width, 1ULL), C);
+ Value *Bits = B.CreateIsNotNull(B.CreateAnd(Shl, BitfieldC), "memchr.bits");
+
+ // Finally merge both checks and cast to pointer type. The inttoptr
+ // implicitly zexts the i1 to intptr type.
+ return B.CreateIntToPtr(B.CreateAnd(Bounds, Bits, "memchr"), CI->getType());
+ }
+
+ // Check if all arguments are constants. If so, we can constant fold.
+ if (!CharC)
+ return nullptr;
+
// Compute the offset.
size_t I = Str.find(CharC->getSExtValue() & 0xFF);
if (I == StringRef::npos) // Didn't find the char. memchr returns null.
Modified: llvm/trunk/test/Transforms/InstCombine/memchr.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/memchr.ll?rev=232902&r1=232901&r2=232902&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/memchr.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/memchr.ll Sat Mar 21 16:09:33 2015
@@ -1,11 +1,14 @@
; Test that the memchr library call simplifier works correctly.
; RUN: opt < %s -instcombine -S | FileCheck %s
-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-f80:128:128"
+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-f80:128:128-n8:16:32"
@hello = constant [14 x i8] c"hello world\5Cn\00"
@hellonull = constant [14 x i8] c"hello\00world\5Cn\00"
@null = constant [1 x i8] zeroinitializer
+ at newlines = constant [3 x i8] c"\0D\0A\00"
+ at single = constant [2 x i8] c"\1F\00"
+ at spaces = constant [4 x i8] c" \0D\0A\00"
@chp = global i8* zeroinitializer
declare i8* @memchr(i8*, i32, i32)
@@ -119,3 +122,67 @@ define void @test9() {
store i8* %dst, i8** @chp
ret void
}
+
+define void @test10() {
+; CHECK-LABEL: @test10
+; CHECK: store i8* null, i8** @chp, align 4
+; CHECK-NOT: call i8* @memchr
+; CHECK: ret void
+
+ %str = getelementptr [14 x i8], [14 x i8]* @hello, i32 0, i32 0
+ %dst = call i8* @memchr(i8* %str, i32 119, i32 6)
+ store i8* %dst, i8** @chp
+ ret void
+}
+
+; Check transformation memchr("\r\n", C, 2) != nullptr -> (C & 9216) != 0
+define i1 @test11(i32 %C) {
+; CHECK-LABEL: @test11
+; CHECK-NEXT: [[TRUNC:%.*]] = trunc i32 %C to i16
+; CHECK-NEXT: %memchr.bounds = icmp ult i16 [[TRUNC]], 16
+; CHECK-NEXT: [[SHL:%.*]] = shl i16 1, [[TRUNC]]
+; CHECK-NEXT: [[AND:%.*]] = and i16 [[SHL]], 9216
+; CHECK-NEXT: %memchr.bits = icmp ne i16 [[AND]], 0
+; CHECK-NEXT: %memchr = and i1 %memchr.bounds, %memchr.bits
+; CHECK-NEXT: ret i1 %memchr
+
+ %dst = call i8* @memchr(i8* getelementptr inbounds ([3 x i8], [3 x i8]* @newlines, i64 0, i64 0), i32 %C, i32 2)
+ %cmp = icmp ne i8* %dst, null
+ ret i1 %cmp
+}
+
+; No 64 bits here
+define i1 @test12(i32 %C) {
+; CHECK-LABEL: @test12
+; CHECK-NEXT: %dst = call i8* @memchr(i8* getelementptr inbounds ([4 x i8], [4 x i8]* @spaces, i32 0, i32 0), i32 %C, i32 3)
+; CHECK-NEXT: %cmp = icmp ne i8* %dst, null
+; CHECK-NEXT: ret i1 %cmp
+
+ %dst = call i8* @memchr(i8* getelementptr inbounds ([4 x i8], [4 x i8]* @spaces, i64 0, i64 0), i32 %C, i32 3)
+ %cmp = icmp ne i8* %dst, null
+ ret i1 %cmp
+}
+
+define i1 @test13(i32 %C) {
+; CHECK-LABEL: @test13
+; CHECK-NEXT: %memchr.bounds = icmp ult i32 %C, 32
+; CHECK-NEXT: [[SHL:%.*]] = shl i32 1, %C
+; CHECK-NEXT: [[AND:%.*]] = and i32 [[SHL]], -2147483647
+; CHECK-NEXT: %memchr.bits = icmp ne i32 [[AND]], 0
+; CHECK-NEXT: %memchr = and i1 %memchr.bounds, %memchr.bits
+; CHECK-NEXT: ret i1 %memchr
+
+ %dst = call i8* @memchr(i8* getelementptr inbounds ([2 x i8], [2 x i8]* @single, i64 0, i64 0), i32 %C, i32 2)
+ %cmp = icmp ne i8* %dst, null
+ ret i1 %cmp
+}
+
+define i1 @test14(i32 %C) {
+; CHECK-LABEL: @test14
+; CHECK-NEXT: icmp eq i32 %C, 31
+; CHECK-NEXT: ret
+
+ %dst = call i8* @memchr(i8* getelementptr inbounds ([2 x i8], [2 x i8]* @single, i64 0, i64 0), i32 %C, i32 1)
+ %cmp = icmp ne i8* %dst, null
+ ret i1 %cmp
+}
Modified: llvm/trunk/test/Transforms/InstCombine/strchr-1.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/strchr-1.ll?rev=232902&r1=232901&r2=232902&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/strchr-1.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/strchr-1.ll Sat Mar 21 16:09:33 2015
@@ -1,10 +1,11 @@
; Test that the strchr library call simplifier works correctly.
; RUN: opt < %s -instcombine -S | FileCheck %s
-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-f80:128:128"
+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-f80:128:128-n8:16:32"
@hello = constant [14 x i8] c"hello world\5Cn\00"
@null = constant [1 x i8] zeroinitializer
+ at newlines = constant [3 x i8] c"\0D\0A\00"
@chp = global i8* zeroinitializer
declare i8* @strchr(i8*, i32)
@@ -76,3 +77,19 @@ define void @test_simplify6(i8* %str) {
store i8* %dst, i8** @chp
ret void
}
+
+; Check transformation strchr("\r\n", C) != nullptr -> (C & 9217) != 0
+define i1 @test_simplify7(i32 %C) {
+; CHECK-LABEL: @test_simplify7
+; CHECK-NEXT: [[TRUNC:%.*]] = trunc i32 %C to i16
+; CHECK-NEXT: %memchr.bounds = icmp ult i16 [[TRUNC]], 16
+; CHECK-NEXT: [[SHL:%.*]] = shl i16 1, [[TRUNC]]
+; CHECK-NEXT: [[AND:%.*]] = and i16 [[SHL]], 9217
+; CHECK-NEXT: %memchr.bits = icmp ne i16 [[AND]], 0
+; CHECK-NEXT: %memchr1 = and i1 %memchr.bounds, %memchr.bits
+; CHECK-NEXT: ret i1 %memchr1
+
+ %dst = call i8* @strchr(i8* getelementptr inbounds ([3 x i8], [3 x i8]* @newlines, i64 0, i64 0), i32 %C)
+ %cmp = icmp ne i8* %dst, null
+ ret i1 %cmp
+}
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