[mips] Make sure loads from lazy-binding entries do not get CSE'd or hoisted out

of loops.

Previously, two consecutive calls to function "func" would result in the
following sequence of instructions:

1. load $16, %got(func)($gp) // load address of lazy-binding stub.
2. move $25, $16
3. jalr $25                  // jump to lazy-binding stub.
4. nop
5. move $25, $16
6. jalr $25                  // jump to lazy-binding stub again.

With this patch, the second call directly jumps to func's address, bypassing
the lazy-binding resolution routine:

1. load $25, %got(func)($gp) // load address of lazy-binding stub.
2. jalr $25                  // jump to lazy-binding stub.
3. nop
4. load $25, %got(func)($gp) // load resolved address of func.
5. jalr $25                  // directly jump to func.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@191591 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 41 insertions, 0 deletions

diff --git a/test/CodeGen/Mips/lazy-binding.ll b/test/CodeGen/Mips/lazy-binding.ll
new file mode 100644
index 0000000..839155a
--- /dev/null
+++ b/test/CodeGen/Mips/lazy-binding.ll
@@ -0,0 +1,41 @@
+; RUN: llc -march=mipsel < %s | FileCheck %s
+
+; CHECK-LABEL: foo6:
+; CHECK: %while.body
+; CHECK: lw  $25, %call16(foo2)(${{[0-9]+}})
+; CHECK: jalr $25
+; CHECK: %while.end
+
+define void @foo6(i32 %n) {
+entry:
+  %tobool1 = icmp eq i32 %n, 0
+  br i1 %tobool1, label %while.end, label %while.body
+
+while.body:                                       ; preds = %entry, %while.body
+  %n.addr.02 = phi i32 [ %dec, %while.body ], [ %n, %entry ]
+  %dec = add nsw i32 %n.addr.02, -1
+  tail call void @foo2()
+  %tobool = icmp eq i32 %dec, 0
+  br i1 %tobool, label %while.end, label %while.body
+
+while.end:                                        ; preds = %while.body, %entry
+  ret void
+}
+
+declare void @foo2()
+
+; CHECK-LABEL: foo1:
+; CHECK: lw $25, %call16(foo2)(${{[0-9]+}})
+; CHECK: jalr $25
+; CHECK: lw $25, %call16(foo2)(${{[0-9]+}})
+; CHECK: jalr $25
+; CHECK: lw $25, %call16(foo2)(${{[0-9]+}})
+; CHECK: jalr $25
+
+define void @foo1() {
+entry:
+  tail call void @foo2()
+  tail call void @foo2()
+  tail call void @foo2()
+  ret void
+}