Improve 64-subtraction of immediates when parts of the immediate can fit
in the literal field of an instruction. E.g.,
long long foo(long long a) {
return a - 734439407618LL;
}
rdar://7038284
llvm-svn: 108339
diff --git a/llvm/lib/Target/ARM/ARMInstrInfo.td b/llvm/lib/Target/ARM/ARMInstrInfo.td
index 59a222c..51fc152 100644
--- a/llvm/lib/Target/ARM/ARMInstrInfo.td
+++ b/llvm/lib/Target/ARM/ARMInstrInfo.td
@@ -1694,13 +1694,19 @@
}
// (sub X, imm) gets canonicalized to (add X, -imm). Match this form.
+// The assume-no-carry-in form uses the negation of the input since add/sub
+// assume opposite meanings of the carry flag (i.e., carry == !borrow).
+// See the definition of AddWithCarry() in the ARM ARM A2.2.1 for the gory
+// details.
def : ARMPat<(add GPR:$src, so_imm_neg:$imm),
(SUBri GPR:$src, so_imm_neg:$imm)>;
-
-//def : ARMPat<(addc GPR:$src, so_imm_neg:$imm),
-// (SUBSri GPR:$src, so_imm_neg:$imm)>;
-//def : ARMPat<(adde GPR:$src, so_imm_neg:$imm),
-// (SBCri GPR:$src, so_imm_neg:$imm)>;
+def : ARMPat<(addc GPR:$src, so_imm_neg:$imm),
+ (SUBSri GPR:$src, so_imm_neg:$imm)>;
+// The with-carry-in form matches bitwise not instead of the negation.
+// Effectively, the inverse interpretation of the carry flag already accounts
+// for part of the negation.
+def : ARMPat<(adde GPR:$src, so_imm_not:$imm),
+ (SBCri GPR:$src, so_imm_not:$imm)>;
// Note: These are implemented in C++ code, because they have to generate
// ADD/SUBrs instructions, which use a complex pattern that a xform function