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For something like
uint32_t hi(uint64_t res) { uint_32t hi = res >> 32; return !hi; } llvm IR looks like this: define i32 @hi(i64 %res) nounwind uwtable ssp { entry: %lnot = icmp ult i64 %res, 4294967296 %lnot.ext = zext i1 %lnot to i32 ret i32 %lnot.ext } The optimizer has optimize away the right shift and truncate but the resulting constant is too large to fit in the 32-bit immediate field. The resulting x86 code is worse as a result: movabsq $4294967296, %rax ## imm = 0x100000000 cmpq %rax, %rdi sbbl %eax, %eax andl $1, %eax This patch teaches the x86 lowering code to handle ult against a large immediate with trailing zeros. It will issue a right shift and a truncate followed by a comparison against a shifted immediate. shrq $32, %rdi testl %edi, %edi sete %al movzbl %al, %eax It also handles a ugt comparison against a large immediate with trailing bits set. i.e. X > 0x0ffffffff -> (X >> 32) >= 1 rdar://11866926 llvm-svn: 160312
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@ -3059,6 +3059,50 @@ static unsigned TranslateX86CC(ISD::CondCode SetCCOpcode, bool isFP,
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RHS = DAG.getConstant(0, RHS.getValueType());
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return X86::COND_LE;
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}
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if (SetCCOpcode == ISD::SETULT || SetCCOpcode == ISD::SETUGE) {
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unsigned TrailZeros = RHSC->getAPIntValue().countTrailingZeros();
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if (TrailZeros >= 32) {
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// The constant doesn't fit in cmp immediate field. Right shift LHS by
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// the # of trailing zeros and truncate it to 32-bit. Then compare
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// against shifted RHS.
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assert(LHS.getValueType() == MVT::i64 && "Expecting a 64-bit cmp!");
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DebugLoc dl = LHS.getDebugLoc();
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LHS = DAG.getNode(ISD::TRUNCATE, dl, MVT::i32,
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DAG.getNode(ISD::SRL, dl, MVT::i64, LHS,
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DAG.getConstant(TrailZeros, MVT::i8)));
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uint64_t C = RHSC->getZExtValue() >> TrailZeros;
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if (SetCCOpcode == ISD::SETULT) {
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// X < 0x300000000 -> (X >> 32) < 3
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// X < 0x100000000 -> (X >> 32) == 0
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// X < 0x200000000 -> (X >> 33) == 0
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if (C == 1) {
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RHS = DAG.getConstant(0, MVT::i32);
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return X86::COND_E;
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}
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RHS = DAG.getConstant(C, MVT::i32);
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return X86::COND_B;
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} else /* SetCCOpcode == ISD::SETUGE */ {
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// X >= 0x100000000 -> (X >> 32) >= 1
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RHS = DAG.getConstant(C, MVT::i32);
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return X86::COND_AE;
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}
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}
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}
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if (SetCCOpcode == ISD::SETUGT) {
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unsigned TrailOnes = RHSC->getAPIntValue().countTrailingOnes();
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if (TrailOnes >= 32 && !RHSC->isAllOnesValue()) {
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assert(LHS.getValueType() == MVT::i64 && "Expecting a 64-bit cmp!");
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DebugLoc dl = LHS.getDebugLoc();
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LHS = DAG.getNode(ISD::TRUNCATE, dl, MVT::i32,
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DAG.getNode(ISD::SRL, dl, MVT::i64, LHS,
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DAG.getConstant(TrailOnes, MVT::i8)));
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uint64_t C = (RHSC->getZExtValue()+1) >> TrailOnes;
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// X > 0x0ffffffff -> (X >> 32) >= 1
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RHS = DAG.getConstant(C, MVT::i32);
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return X86::COND_AE;
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}
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}
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}
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switch (SetCCOpcode) {
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@ -12,9 +12,9 @@ declare hidden fastcc void @_ZN3JSCL23returnToThrowTrampolineEPNS_12JSGlobalData
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; Avoid hoisting the test above loads or copies
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; CHECK: %entry
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; CHECK: cmpq
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; CHECK: test
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; CHECK-NOT: mov
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; CHECK: jb
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; CHECK: je
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define i32 @cti_op_eq(i8** nocapture %args) nounwind ssp {
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entry:
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%0 = load i8** null, align 8
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@ -90,3 +90,51 @@ F:
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; CHECK: encoding: [0x48,0x83,0x7c,0x24,0xf8,0x00]
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}
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; rdar://11866926
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define i32 @test7(i64 %res) nounwind uwtable readnone ssp {
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entry:
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; CHECK: test7:
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; CHECK-NOT: movabsq
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; CHECK: shrq $32, %rdi
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; CHECK: testl %edi, %edi
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; CHECK: sete
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%lnot = icmp ult i64 %res, 4294967296
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%lnot.ext = zext i1 %lnot to i32
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ret i32 %lnot.ext
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}
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define i32 @test8(i64 %res) nounwind uwtable readnone ssp {
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entry:
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; CHECK: test8:
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; CHECK-NOT: movabsq
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; CHECK: shrq $32, %rdi
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; CHECK: cmpl $3, %edi
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%lnot = icmp ult i64 %res, 12884901888
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%lnot.ext = zext i1 %lnot to i32
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ret i32 %lnot.ext
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}
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define i32 @test9(i64 %res) nounwind uwtable readnone ssp {
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entry:
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; CHECK: test9:
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; CHECK-NOT: movabsq
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; CHECK: shrq $33, %rdi
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; CHECK: testl %edi, %edi
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; CHECK: sete
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%lnot = icmp ult i64 %res, 8589934592
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%lnot.ext = zext i1 %lnot to i32
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ret i32 %lnot.ext
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}
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define i32 @test10(i64 %res) nounwind uwtable readnone ssp {
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entry:
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; CHECK: test10:
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; CHECK-NOT: movabsq
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; CHECK: shrq $32, %rdi
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; CHECK: cmpl $1, %edi
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; CHECK: setae
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%lnot = icmp uge i64 %res, 4294967296
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%lnot.ext = zext i1 %lnot to i32
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ret i32 %lnot.ext
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}
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