Check to make sure that the iterator isn't at the beginning of the basic block

before decrementing. <rdar://problem/8529919>

llvm-svn: 116126

lib/Target/ARM/ARMBaseInstrInfo.cpp

@@ -1528,6 +1528,10 @@ OptimizeCompareInstr(MachineInstr *CmpInstr, unsigned SrcReg, int CmpMask,
   // want to change.
   MachineBasicBlock::const_iterator I = CmpInstr, E = MI,
     B = MI->getParent()->begin();
+
+  // Early exit if CmpInstr is at the beginning of the BB.
+  if (I == B) return false;
+
   --I;
   for (; I != E; --I) {
     const MachineInstr &Instr = *I;

test/CodeGen/ARM/2010-10-08-PeepholeCrash.ll

@@ -0,0 +1,118 @@
+; RUN: llc < %s -mtriple=thumbv7-apple-darwin10
+; <rdar://problem/8529919>
+
+%struct.GLDLightProduct = type { %struct.GLIColor4, %struct.GLIColor4, %struct.GLIColor4 }
+%struct.GLDPointLineLimits = type { float, float, float }
+%struct.GLIColor4 = type { float, float, float, float }
+%struct.__GLmaterial = type { %struct.GLIColor4, %struct.GLIColor4, %struct.GLIColor4, %struct.GLIColor4, float, float, float, float, [8 x %struct.GLDLightProduct], %struct.GLIColor4, %struct.__GLsum, i32, %struct.__GLmaterial*, %struct.__GLmaterial*, [4 x i32] }
+%struct.__GLsum = type { %struct.GLIColor4, i8, i8, i8, i8 }
+%struct.__GLvertex = type { %struct.GLIColor4, %struct.GLIColor4, %struct.GLIColor4, %struct.GLIColor4, %struct.GLIColor4, %struct.GLDPointLineLimits, float, %struct.GLIColor4, float, i8, i8, i8, i8, float, float, i32, i32, i32, [4 x i8], [4 x float], [2 x %struct.__GLmaterial*], i32, i32, [32 x %struct.GLIColor4], [2 x %struct.GLIColor4] }
+
+define void @func() nounwind {
+entry:
+  %0 = load i32* undef, align 4
+  br i1 undef, label %gleLLVMVecPrimMulti.exit, label %bb.i9
+
+bb.i9:                                            ; preds = %entry
+  switch i32 undef, label %bb3.i11 [
+    i32 4, label %bb8.i
+    i32 8, label %bb5.i
+  ]
+
+bb3.i11:                                          ; preds = %bb.i9
+  br label %bb8.i
+
+bb5.i:                                            ; preds = %bb.i9
+  br label %bb8.i
+
+bb8.i:                                            ; preds = %bb5.i, %bb3.i11, %bb.i9
+  br i1 undef, label %gleLLVMVecPrimMulti.exit, label %bb12.i
+
+bb12.i:                                           ; preds = %bb8.i
+  br i1 undef, label %bb15.i, label %bb13.i
+
+bb13.i:                                           ; preds = %bb12.i
+  br i1 undef, label %bb16.i, label %bb14.i
+
+bb14.i:                                           ; preds = %bb13.i
+  unreachable
+
+bb15.i:                                           ; preds = %bb12.i
+  unreachable
+
+bb16.i:                                           ; preds = %bb13.i
+  br i1 undef, label %bb18.i, label %bb17.i
+
+bb17.i:                                           ; preds = %bb16.i
+  br label %bb18.i
+
+bb18.i:                                           ; preds = %bb17.i, %bb16.i
+  br i1 undef, label %bb19.i, label %gleLLVMVecPrimMulti.exit
+
+bb19.i:                                           ; preds = %bb18.i
+  %1 = and i32 %0, 16
+  %2 = icmp eq i32 %1, 0
+  %invok.1.i = select i1 %2, i32 undef, i32 0
+  br i1 undef, label %bb27.i, label %bb26.i
+
+bb26.i:                                           ; preds = %bb19.i
+  unreachable
+
+bb27.i:                                           ; preds = %bb19.i
+  br i1 undef, label %bb29.i, label %bb28.i
+
+bb28.i:                                           ; preds = %bb27.i
+  unreachable
+
+bb29.i:                                           ; preds = %bb27.i
+  br i1 false, label %bb360.preheader.i, label %bb30.i
+
+bb30.i:                                           ; preds = %bb29.i
+  unreachable
+
+bb360.preheader.i:                                ; preds = %bb29.i
+  %tmp119 = add i32 %invok.1.i, 0
+  br i1 undef, label %bb32.i, label %gleLLVMVecPrimMulti.exit
+
+bb32.i:                                           ; preds = %bb360.preheader.i
+  br label %bb179.i
+
+bb179.i:                                          ; preds = %bb216.i, %bb32.i
+  %tmp120 = add i32 %tmp119, 0
+  br i1 undef, label %bb181.i, label %bb180.i
+
+bb180.i:                                          ; preds = %bb179.i
+  %scevgep810.i = getelementptr %struct.__GLvertex* null, i32 %tmp120, i32 15
+  store i32 undef, i32* %scevgep810.i, align 4
+  br label %bb181.i
+
+bb181.i:                                          ; preds = %bb180.i, %bb179.i
+  switch i32 undef, label %bb216.i [
+    i32 4, label %bb187.i
+    i32 6, label %bb197.i
+  ]
+
+bb187.i:                                          ; preds = %bb181.i
+  br label %bb216.i
+
+bb197.i:                                          ; preds = %bb181.i
+  br i1 %2, label %bb199.i, label %bb198.i
+
+bb198.i:                                          ; preds = %bb197.i
+  br label %bb216.i
+
+bb199.i:                                          ; preds = %bb197.i
+  br label %bb216.i
+
+bb216.i:                                          ; preds = %bb199.i, %bb198.i, %bb187.i, %bb181.i
+  br label %bb179.i
+
+gleLLVMVecPrimMulti.exit:                         ; preds = %bb360.preheader.i, %bb18.i, %bb8.i, %entry
+  br i1 undef, label %gleLLVMVecCleanMaterials.exit, label %bb2
+
+bb2:                                              ; preds = %gleLLVMVecPrimMulti.exit
+  ret void
+
+gleLLVMVecCleanMaterials.exit:                    ; preds = %gleLLVMVecPrimMulti.exit
+  ret void
+}