vulkan: Handle FA with all -inf mask values (ggml-org#16447)

Author: jeffbolznv

ggml/src/ggml-vulkan/vulkan-shaders/flash_attn.comp

@@ -345,7 +345,7 @@ void main() {
 
     float Lfrcp[Br];
     [[unroll]] for (uint32_t r = 0; r < Br; ++r) {
-        Lfrcp[r] = 1.0 / Lf[r];
+        Lfrcp[r] = (Lf[r] == 0.0) ? 0.0 : (1.0 / Lf[r]);
     }
 
     [[unroll]] for (uint32_t d = 0; d < HSV_per_thread / 4; ++d) {

ggml/src/ggml-vulkan/vulkan-shaders/flash_attn_cm1.comp

@@ -380,7 +380,7 @@ void main() {
 
     float Lfrcp[rows_per_thread];
     [[unroll]] for (uint32_t r = 0; r < rows_per_thread; ++r) {
-        Lfrcp[r] = 1.0 / Lf[r];
+        Lfrcp[r] = (Lf[r] == 0.0) ? 0.0 : (1.0 / Lf[r]);
     }
 
     [[unroll]] for (uint32_t d = 0; d < HSV_per_thread / 4; ++d) {

ggml/src/ggml-vulkan/vulkan-shaders/flash_attn_cm2.comp

@@ -121,7 +121,11 @@ void main() {
     const float NEG_FLT_MAX_OVER_2 = uintBitsToFloat(0xFEFFFFFF);
 
     L = coopmat<ACC_TYPE, gl_ScopeWorkgroup, Br, Bc, gl_MatrixUseAccumulator>(0);
+#if defined(ACC_TYPE_MAX)
+    M = coopmat<ACC_TYPE, gl_ScopeWorkgroup, Br, Bc, gl_MatrixUseAccumulator>(-ACC_TYPE_MAX / ACC_TYPE(2));
+#else
     M = coopmat<ACC_TYPE, gl_ScopeWorkgroup, Br, Bc, gl_MatrixUseAccumulator>(NEG_FLT_MAX_OVER_2);
+#endif
 
     coopmat<ACC_TYPE, gl_ScopeWorkgroup, Br, Bc, gl_MatrixUseAccumulator> slopeMat = coopmat<ACC_TYPE, gl_ScopeWorkgroup, Br, Bc, gl_MatrixUseAccumulator>(1.0);
 
@@ -294,7 +298,7 @@ void main() {
 
     [[unroll]]
     for (int k = 0; k < Ldiag.length(); ++k) {
-        Ldiag[k] = ACC_TYPE(1.0) / Ldiag[k];
+        Ldiag[k] = (Ldiag[k] == 0.0) ? ACC_TYPE(0.0) : (ACC_TYPE(1.0) / Ldiag[k]);
     }
 
     O = Ldiag*O;

ggml/src/ggml-vulkan/vulkan-shaders/flash_attn_split_k_reduce.comp

@@ -91,7 +91,7 @@ void main() {
         L = L*ms + vs;
     }
 
-    L = 1.0 / L;
+    L = (L == 0.0) ? 0.0 : 1.0 / L;
 
     // D dimension is split across workgroups in the y dimension
     uint d = tid + gl_WorkGroupID.y * BLOCK_SIZE;