The code pattern "imm0_255_neg" is used for checking if an immediate value is a small negative number.

This patch changes the definition of negative from -0..-255 to -1..-255. I am changing this because of
a bug that we had in some of the patterns that assumed that "subs" of zero does not set the carry flag.

rdar://12028498

llvm-svn: 167963

2 files changed, 38 insertions, 6 deletions

diff --git a/llvm/lib/Target/ARM/ARMInstrThumb2.td b/llvm/lib/Target/ARM/ARMInstrThumb2.td
index 002d64a2d03..d40a0746f85 100644
--- a/llvm/lib/Target/ARM/ARMInstrThumb2.td
+++ b/llvm/lib/Target/ARM/ARMInstrThumb2.td
@@ -130,8 +130,9 @@ def imm0_4095_neg : Operand<i32>, PatLeaf<(i32 imm), [{
   let ParserMatchClass = imm0_4095_neg_asmoperand;
 }
 
-def imm0_255_neg : PatLeaf<(i32 imm), [{
-  return (uint32_t)(-N->getZExtValue()) < 255;
+def imm1_255_neg : PatLeaf<(i32 imm), [{
+  uint32_t Val = -N->getZExtValue();
+  return (Val > 0 && Val < 255);
 }], imm_neg_XFORM>;
 
 def imm0_255_not : PatLeaf<(i32 imm), [{
@@ -1928,8 +1929,8 @@ defm t2RSBS : T2I_rbin_s_is <BinOpFrag<(ARMsubc node:$LHS, node:$RHS)>>;
 // The AddedComplexity preferences the first variant over the others since
 // it can be shrunk to a 16-bit wide encoding, while the others cannot.
 let AddedComplexity = 1 in
-def : T2Pat<(add        GPR:$src, imm0_255_neg:$imm),
-            (t2SUBri    GPR:$src, imm0_255_neg:$imm)>;
+def : T2Pat<(add        GPR:$src, imm1_255_neg:$imm),
+            (t2SUBri    GPR:$src, imm1_255_neg:$imm)>;
 def : T2Pat<(add        GPR:$src, t2_so_imm_neg:$imm),
             (t2SUBri    GPR:$src, t2_so_imm_neg:$imm)>;
 def : T2Pat<(add        GPR:$src, imm0_4095_neg:$imm),
@@ -1938,8 +1939,8 @@ def : T2Pat<(add        GPR:$src, imm0_65535_neg:$imm),
             (t2SUBrr    GPR:$src, (t2MOVi16 (imm_neg_XFORM imm:$imm)))>;
 
 let AddedComplexity = 1 in
-def : T2Pat<(ARMaddc    rGPR:$src, imm0_255_neg:$imm),
-            (t2SUBSri   rGPR:$src, imm0_255_neg:$imm)>;
+def : T2Pat<(ARMaddc    rGPR:$src, imm1_255_neg:$imm),
+            (t2SUBSri   rGPR:$src, imm1_255_neg:$imm)>;
 def : T2Pat<(ARMaddc    rGPR:$src, t2_so_imm_neg:$imm),
             (t2SUBSri   rGPR:$src, t2_so_imm_neg:$imm)>;
 def : T2Pat<(ARMaddc    rGPR:$src, imm0_65535_neg:$imm),
diff --git a/llvm/test/CodeGen/ARM/2012-11-14-subs_carry.ll b/llvm/test/CodeGen/ARM/2012-11-14-subs_carry.ll
new file mode 100644
index 00000000000..38700f3a8d1
--- /dev/null
+++ b/llvm/test/CodeGen/ARM/2012-11-14-subs_carry.ll
@@ -0,0 +1,31 @@
+; RUN: llc < %s -mtriple=thumbv7-apple-ios | FileCheck %s
+
+;CHECK: foo
+;CHECK: adds
+;CHECK-NEXT: adc
+;CHECK-NEXT: bx
+
+;rdar://12028498
+
+define i32 @foo() nounwind ssp {
+entry:
+  %tmp2 = zext i32 3 to i64
+  br  label %bug_block
+
+bug_block:
+  %tmp410 = and i64 1031, 1647010
+  %tmp411 = and i64 %tmp2, -211
+  %tmp412 = shl i64 %tmp410, %tmp2
+  %tmp413 = shl i64 %tmp411, %tmp2
+  %tmp415 = and i64 %tmp413, 1
+  %tmp420 = xor i64 0, %tmp415
+  %tmp421 = and i64 %tmp412, %tmp415
+  %tmp422 = shl i64 %tmp421, 1
+  br  label %finish
+
+finish:
+  %tmp423 = lshr i64 %tmp422, 32
+  %tmp424 = trunc i64 %tmp423 to i32
+  ret i32 %tmp424
+}
+