[AVR] Add test for issue #1

Author: Dylan McKay

test/CodeGen/AVR/high-pressure-on-ptrregs.ll

@@ -0,0 +1,82 @@
+; RUN: llc < %s -march=avr | FileCheck %s
+
+; This tests how LLVM handles IR which puts very high
+; presure on the PTRREGS class for the register allocator.
+;
+; This causes a problem because we only have one small register
+; class for loading and storing from pointers - 'PTRREGS'.
+; One of these registers is also used for the frame pointer, meaning
+; that we only ever have two registers available for these operations.
+;
+; There is an existing bug filed for this issue - PR14879.
+;
+; LLVM should be able to handle this elegantly, because PTRREGS is a
+; subset of DREGS, so we should be able to do cross-class copies in
+; order to complete register allocation.
+;
+; The specific failure:
+; LLVM ERROR: ran out of registers during register allocation
+;
+; It has been assembled from the following c code:
+;
+; struct ss
+; {
+;   int a;
+;   int b;
+;   int c;
+; };
+;
+; void loop(struct ss *x, struct ss **y, int z)
+; {
+;   int i;
+;   for (i=0; i<z; ++i)
+;   {
+;     x->c += y[i]->b;
+;   }
+; }
+
+%struct.ss = type { i16, i16, i16 }
+
+; CHECK-LABEL: loop
+define void @loop(%struct.ss* %x, %struct.ss** %y, i16 %z) {
+entry:
+  %x.addr = alloca %struct.ss*, align 2
+  %y.addr = alloca %struct.ss**, align 2
+  %z.addr = alloca i16, align 2
+  %i = alloca i16, align 2
+  store %struct.ss* %x, %struct.ss** %x.addr, align 2
+  store %struct.ss** %y, %struct.ss*** %y.addr, align 2
+  store i16 %z, i16* %z.addr, align 2
+  store i16 0, i16* %i, align 2
+  br label %for.cond
+
+for.cond:                                         ; preds = %for.inc, %entry
+  %0 = load i16, i16* %i, align 2
+  %1 = load i16, i16* %z.addr, align 2
+  %cmp = icmp slt i16 %0, %1
+  br i1 %cmp, label %for.body, label %for.end
+
+for.body:                                         ; preds = %for.cond
+  %2 = load i16, i16* %i, align 2
+  %3 = load %struct.ss**, %struct.ss*** %y.addr, align 2
+  %arrayidx = getelementptr inbounds %struct.ss*, %struct.ss** %3, i16 %2
+  %4 = load %struct.ss*, %struct.ss** %arrayidx, align 2
+  %b = getelementptr inbounds %struct.ss, %struct.ss* %4, i32 0, i32 1
+  %5 = load i16, i16* %b, align 2
+  %6 = load %struct.ss*, %struct.ss** %x.addr, align 2
+  %c = getelementptr inbounds %struct.ss, %struct.ss* %6, i32 0, i32 2
+  %7 = load i16, i16* %c, align 2
+  %add = add nsw i16 %7, %5
+  store i16 %add, i16* %c, align 2
+  br label %for.inc
+
+for.inc:                                          ; preds = %for.body
+  %8 = load i16, i16* %i, align 2
+  %inc = add nsw i16 %8, 1
+  store i16 %inc, i16* %i, align 2
+  br label %for.cond
+
+for.end:                                          ; preds = %for.cond
+  ret void
+}
+